a verb that does not add -ed to form the past tense

a verb which does not conform to an expected inflectional pattern, derivation, or word formation

A verb that forms the simple past in a different way than regular verbs. Some irregular verbs use the simple form as their simple past and past participle form (put put - put); others have one irregular form for both the simple past and the past participle (buy - bought - bought); and others have different simple past and past participle forms (sing - sang - sung).

see verb.

A verb which does not follow standard rules for conjugation

In contrast to regular verbs, irregular verbs are those verbs that fall outside the standard patterns of conjugation in the languages in which they occur.