Heteroclite

Part of speech: noun (n.)

1. 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.

2. Any thing or person deviating from the common rule, or from common forms. Howell.

Part of speech: adjective (a.)

Deviating from ordinary forms or rules; irregular; anomalous; abnormal.