The English word militant is both an adjective and a noun, and it is generally used to mean vigorously active, combative and/or aggressive, especially in support of a cause, as in "militant reformers".   It comes from the 15th century Latin "militare" meaning "to serve as a soldier". The related modern concept of the militia as a defensive organization against invaders grew out of the Anglo-Saxon fyrd. In times of crisis, the militiaman left his civilian duties and became a soldier until the emergency was over, when he returned to his civilian occupation.
The current meaning of militant does not usually refer to a registered soldier: it can be anyone who subscribes to the idea of using vigorous, sometimes extreme, activity to achieve an objective, usually political. A "militant [political] activist" would be expected to be more confrontational and aggressive than an activist not described as militant.
Militance may or may not include physical violence, armed combat, terrorism, and the like. The Trotskyist Militant group in the United Kingdom published a newspaper, was active in labour disputes, moved resolutions in political meetings, but was not based on violence. The purpose of the Christian Church Militant is to struggle against sin, the devil and ". . . the rulers of the darkness of this world, against spiritual wickedness in high places" (Ephesians 6:12), but it is not a violent movement.
Militant can mean "vigorously active and aggressive, especially in support of a cause" as in 'militant reformers'.  The American Heritage Dictionary of the English Language, defines militant as "Having a combative character; aggressive, especially in the service of a cause". The Merriam-Webster Dictionary defines militant as "aggressively active (as in a cause)".  It says that the word militant might typically be used in phrases such as 'militant conservationists' or 'a militant attitude'. 
An example of the adjective usages is demonstrated when The New York Times ran an article titled Militant Environmentalists Planning Summer Protests to Save Redwoods describing a group that believes in "confrontational demonstrations" and "nonviolent tactics" to get across their message of preserving the environment.  Another usage example includes 'a militant political activist',  drawing attention to behaviours typical of those engaged in intensive political activism. The political protests headed by the Reverend Al Sharpton have been described as militant in nature in The Washington Post . 
In general usage, a militant person is a confrontational person who does not necessarily use violence.
Militant is often used within some religious circles to denote the continuous battle of Christians (as church members) or the Christian Church in their struggle against sin. In particular, the Roman Catholic Church differentiates between Church militant and church triumphant.   Ellen G. White, one of the founders of the Seventh-day Adventist church, says "Now the church is militant. Now we are confronted with a world in darkness, almost wholly given over to idolatry." 
Such religious meaning must not be confused with the word 'belligerent' used to describe extremist religious behaviours found in some who, based on their extreme religious beliefs or ideologies, take up weapons and become involved in warfare, or who commit acts of violence or terrorism in an attempt to advance their extremist religious agendas. Such extremist groups can be Christian,   Muslims,    Jewish,    or of any other religious affiliation.
A militant, as a noun, is a person who uses militant methods in pursuit of an objective;  the term is not associated with the military. Militant can refer to an individual displaying aggressive behavior or attitudes.
Militant is sometimes used as a euphemism for terrorist or armed insurgent.  (For more on this, see mass media usage below.)
The word "militant" is sometimes used to describe groups that do not name or describe themselves as militants, but that advocate extreme violence. In the early 21st century, members of groups involved in Islamic terrorism such as Al-Qaeda and ISIS are usually described as militants. 
Newspapers, magazines, and other information sources may deem militant a neutral term,  whereas terrorist  or guerrilla  conventionally indicates disapproval of the behavior of the individual or organization so labeled, regardless of the motivations for such behavior. Militant, at other times, can refer to anyone not a member of formal armed forces engaging in warfare or serving as a combatant.
The mass media sometimes uses the term "militant" in the context of terrorism.  Journalists sometimes apply the term militant to paramilitary movements using terrorism as a tactic. The mass media also has used the term militant groups or radical militants for terrorist organizations.   
Those resisting a foreign military occupation can be seen as not meriting the label terrorists because their acts of political violence against military targets of a foreign occupier do not violate international law. Protocol 1 of the Geneva Conventions gives lawful combatant status to those engaging in armed conflicts against alien (or foreign) occupation, colonial domination and racist régimes. Non-uniformed guerrillas also gain combatant status if they carry arms openly during military operations. Protocol 1 does not legitimize attacks on civilians by militants who fall into these categories.
In the UN General Assembly Resolution on terrorism (42/159, 7 December 1987). which condemns international terrorism and outlines measures to combat the crime, with one proviso: "that nothing in the present resolution could in any way prejudice the right to self-determination, freedom and independence, as derived from the Charter of the United Nations, of peoples forcibly deprived of that right [...], particularly peoples under colonial and racist regimes and foreign occupation or other forms of colonial domination, nor...the right of these peoples to struggle to this end and to seek and receive support [in accordance with the Charter and other principles of international law]."
Militants occur across the political spectrum, including racial or religious supremacists, separatists, abortion opponents and proponents, and environmentalists. Examples of left-wing, right-wing, and advocacy group militants include militant reformers, militant feminists, militant animal rights advocates, and militant anarchists. The phrase militant Islam can suggest violent and aggressive political activity by Islamic individuals, groups, movements, or governments. There are also various secret societies that are classified as militant groups.[ citation needed ]
Using the president's authority to assassinate people worldwide who pose an "imminent threat" if "capture is not feasible",  [ better source needed ] the Obama administration routinely called every victim of extrajudicial killing a militant. 
Among organisations that describe themselves as militants, the Ulster Young Militants are an example of a group resorting to violence (intimidation, arson, and murder) as a deliberate tactic.
Militant research is defined as a type of research that is distinct from academia while also not synonymous with the political militant. It refuses the alienating practices of academia which separate researchers from the political meaning of their activity.  In recent years it has become an increasingly popular approach for doing research  especially since it attempt to resolve academic concerns related to representation and auto-critique. 
Compare and contrast these related articles:
State terrorism refers to acts of terrorism which a state conducts against another state or against its own citizens.
Terrorism, in its broadest sense, is the use of intentional violence and fear to achieve political or ideological aims. The term is used in this regard primarily to refer to intentional violence during peacetime or in the context of war against non-combatants. The terms "terrorist" and "terrorism" originated during the French Revolution of the late 18th century but became widely used internationally and gained worldwide attention in the 1970s during the Troubles in Northern Ireland, the Basque conflict, and the Israeli–Palestinian conflict. The increased use of suicide attacks from the 1980s onwards was typified by the 2001 September 11 attacks in the United States.
Jamaat Ansar al-Sunnah, also known as Jaish Ansar al-Sunna, Ali ibn Abi Talib Battalion or simply as Ansar al-Sunnah was an Iraqi Sunni insurgent group that fought against US troops and their local allies during the Iraq War. The group was primarily based in northern and central Iraq, and included mostly Iraqi fighters. In 2007, it split; with its Kurdish members pledging allegiance to Ansar al-Islam, and its Arab members creating a group called Ansar al-Sunnah Shariah Committee, before changing its name to Ansar al-Ahlu Sunnah in 2011.
There is no universal agreement on the legal definition of terrorism, although there exists a consensus academic definition created by scholars.
Islamic terrorism refers to terrorist acts with religious motivations carried out by fundamentalist militant Islamists and Islamic extremists.
Christian terrorism, a form of religious terrorism, comprises terrorist acts which are committed by groups or individuals who profess Christian motivations or goals. Christian terrorists justify their violent tactics through their interpretation of the Bible and Christianity, in accordance with their own objectives and worldview.
Fourth-generation warfare (4GW) is conflict characterized by a blurring of the lines between war and politics, combatants and civilians.
Terrorism in India, according to the Home Ministry, poses a significant threat to the people of India. Compared to other countries, India faces a wide range of terror groups. Terrorism found in India includes Islamic terrorism, separatist terrorism, and left-wing terrorism India is one of the countries most impacted by terrorism.
Palestinian political violence refers to acts of violence perpetrated for political ends in relation to the State of Palestine or in connection with Palestinian nationalism. Common political objectives include self-determination in and sovereignty over Palestine, or the "liberation of Palestine" and recognition of a Palestinian state, either in place of both Israel and the Palestinian territories, or solely in the Palestinian territories. More limited goals include the release of Palestinian prisoners or the Palestinian right of return. Other motivations include personal grievances, trauma or revenge.
Jewish religious terrorism is religious terrorism committed by extremists within Judaism.
Left-wing terrorism or far-left terrorism is terrorism motivated by left-wing or far-left ideologies, committed with the aim of overthrowing current capitalist systems and replacing them with communist or socialist societies. Left-wing terrorism can also occur within already socialist states as criminal action against the current ruling government.
The history of terrorism is a history of well-known and historically significant individuals, entities, and incidents associated, whether rightly or wrongly, with terrorism. Scholars agree that terrorism is a disputed term, and very few of those labeled terrorists describe themselves as such. It is common for opponents in a violent conflict to describe the other side as terrorists or as practicing terrorism.
The internal conflict in Peru is an ongoing armed conflict between the Government of Peru and the Maoist guerilla group Shining Path. The conflict began on 17 May 1980, and from 1982 to 1997 the Túpac Amaru Revolutionary Movement waged its own insurgency as a Marxist–Leninist rival to the Shining Path.
Communist terrorism is terrorism perpetrated by individuals or groups which adhere to communism and ideologies related to it, such as Marxism–Leninism, Maoism, and Trotskyism. Historically, communist terrorism has sometimes taken the form of state-sponsored terrorism, supported by communist nations such as the Soviet Union, China, North Korea and Cambodia. In addition, non-state actors such as the Red Brigades, the Front Line and the Red Army Faction have also engaged in communist terrorism. These groups hope to inspire the masses to rise up and start a revolution to overthrow existing political and economic systems. This form of terrorism can sometimes be called red terrorism or left-wing terrorism.
In international relations, violent non-state actors (VNSAs), also known as non-state armed actors or non-state armed groups (NSAGs), are individuals or groups that are wholly or partly independent of governments and which threaten or use violence to achieve their goals.
Political violence is violence which is perpetrated in order to achieve political goals. It can include violence which is used by a state against other states (war), violence which is used by a state against civilians and non-state actors, and violence which is used by violent non-state actors against states and civilians. It can also describe politically motivated violence which is used by violent non-state actors against a state or it can describe violence which is used against other non-state actors and/or civilians. Non-action on the part of a government can also be characterized as a form of political violence, such as refusing to alleviate famine or otherwise denying resources to politically identifiable groups within their territory.
The following outline is provided as an overview of and topical guide to the past and present terrorism in the United States:
Terrorism in Sri Lanka has been a highly destructive phenomenon during the periods of the Sri Lankan Civil War (1983–2009) and the first and second JVP insurrections. A common definition of terrorism is the systematic use or threatened use of violence to intimidate a population or government for political, religious, or ideological goals. Sri Lanka is a country that has experienced some of the worst known acts of modern terrorism, such as suicide bombings, massacres of civilians and assassination of political and social leaders, that posed a significant threat to the society, economy and development of the country. The Prevention of Terrorism Act of 1978 is the legislation, that provides the powers to law enforcement officers to deal with issues related to terrorism in Sri Lanka. It was first enacted as a temporary law in 1979 under the presidency of J. R. Jayewardene, and later made permanent in 1982.
Domestic terrorism or homegrown terrorism is a form of terrorism in which victims "within a country are targeted by a perpetrator with the same citizenship" as the victims. There are many definitions of terrorism, and none of them are universally accepted.