Final answer:
The word 'say' is the irregular verb.
Step-by-step explanation:
An irregular verb is a verb that does not follow the regular conjugation pattern in the past tense and past participle forms. Out of the given options, the word 'say' is the irregular verb. The past tense form of 'say' is 'said' and its past participle form is also 'said', which does not follow the usual -ed ending for regular verbs. For example:
I said hello to him yesterday.
She has said nothing about it.
Learn more about Irregular verbs