basilect

noun

1. A variety of a language that differs substantially from the standard form, and is only considered suitable for very informal contexts by speakers.

   “The highest level of good English has been called the acrolect; the lowest level of poor speech, the basilect; both are contrasted with the matrilect, the general native language.”

   “In both regions English is used extensively, the spoken form ranging from, in the language of linguisticians, the basilect to the mesolect and the matrilect or acrolect (prestige English) .”

   “If only the basilect is a true creole, then the mesolect is relegated to limbo -- not a creole, certainly not a standard.”