Definition of “affirm” - Learner’s Dictionary

affirm

verb [ T ] uk us /əˈfɜːm/ formal

to say that something is true:

He gave a speech affirming the government's commitment to education.
affirmation uk us /ˌæfəˈmeɪʃən/ noun [ C, U ]

(Definition of “affirm” from the Cambridge Learner's Dictionary © Cambridge University Press)