Definition - A spoken language's most formal register, e.g. the one that is used during important ritual occasions.

Example -
In My Fair Lady, Eliza grows up speaking the London basilect (e.g. "Just you wait 'enry 'iggens, just you wait!"). Henry Higgens succeeds in teaching her the corresponding acrolect (e.g. "In Hartford, Hereford, and Hampshire, hurricanes hardly happen").

Etymology -
The term was coined by linguist Derek Bickerton in the early 1970s who combined the Greek akros, highest or upper, with the word dialect.

Oxford English Dictionary -
The first full citation of the term is from 1977:
"Speakers in a post-creole community are triply pressured:
to avoid the basilect, to acquire the acrolect, and to vary the mesolect."
(Language LIII. 330 )

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