Eau is a trigraph which occurs in some languages that use the Latin script, such as French and English.
In Modern French, ⟨eau⟩ is pronounced /o/ [1] and often appears at the end of a word. Generally, ⟨eau⟩ alternates with ⟨e⟩ in another form of a word, for example, the feminine of chameau (camel) is chamelle. There are three main ways of spelling /o/: ⟨o⟩, ⟨au⟩, and ⟨eau⟩, out of which ⟨eau⟩ is by far the rarest. [2]
In Old French, ⟨eau⟩ represented a triphthong, probably pronounced [e̯aɯ̯] (or [ə̯aɯ̯]). This triphthong originated from the Proto-French diphthong [ɛɯ̯], which had formed from the sequence of ⟨e⟩ and ⟨l⟩, where L had vocalized. In the 12th and 13th centuries, both ⟨iau⟩ and ⟨eau⟩ were used ([i̯aɯ̯] was probably a variant pronunciation), but ⟨eau⟩ soon became the standard spelling. [3] Eau is also a word in French.
In English, ⟨eau⟩ only exists in words borrowed from French, and so is pronounced similarly in almost all cases (like in plateau , bureau ). Exceptions include beauty and words derived from it, where it is pronounced /juː/, bureaucrat where it is pronounced /ə/, bureaucracy where it is pronounced /ɒ/, [4] and (in some contexts) the proper names Beaulieu and Beauchamp (as /juː/ and /iː/, respectively). [5]