noun
: a distribution of a pair of speech sounds or a pair of linguistic forms such that the one is found only in environments where the other is not (as the unaspirated t of English stone and the aspirated t of English tone or English your occurring before a noun, yours in all other environments), especially when used as a basic prerequisite for the classification of nonidentical sounds as allophones of the same phoneme or for the classification of nonidentical linguistic forms as allomorphs of the same morpheme