A verb that is not inflected in the usual way—for example, by the addition of -ed to the root form to create the past tense and past participle. There are five common types of irregular verbs classified according to how they indicate past tense and past participle: vowel changes (begin, began, begun); -en added (beat, beat, beaten); vowel changes (spin, spun, spun); -d changes to -t (lend, lent, lent); no change (put, put, put).