Heterocliton, in grammar, an irregular or anomalous word, which either in declension, conjugation, or regimen, deviates from the ordinary rules of grammar. The word is Greek, ἑτερογένεια, formed of ἑτερός, "another, different," and γένος, "I decline."

Heteroclyte is more peculiarly applied to nouns which vary or are irregular in point of declension; having fewer cases, numbers, &c. than ordinary; or that are of one declension in one number, and another in another; as, ἡ ἀκαδημία, ἡ ἀκαδημία, ἡ ἀκαδημία, ἡ ἀκαδημία.