(1):

(a.) Deviating from ordinary forms or rules; irregular; anomalous; abnormal.

(2):

(n.) A word which is irregular or anomalous either in declension or conjugation, or which deviates from ordinary forms of inflection in words of a like kind; especially, a noun which is irregular in declension.

(3):

(n.) Any thing or person deviating from the common rule, or from common forms.