In linguistics, a basilect is a term for dialects of speech which have diverged so far from the standard language that in essence they have become a different language. A basilect represents the opposite end of the scale of linguistic formality from an acrolect.

Basilects typically differ from the standard language in pronunciation, vocabulary, and grammar, and can often develop into different languages, as the basilects of Vulgar Latin eventually developed into Romance languages.

Ebonics may be seen as a modern example of a basilect.