Synonyms of certifying

1 Syllable
show, vouch, swear
2 Syllables
avow, aver, profess, witness, confirm, okay, attest, state, sanction
3 Syllables
endorse, testify, guarantee, rubber-stamp, notify, ascertain, commission, accredit, license, assure, approve, reassure, verify
4 Syllables
authorize, validate
5 Syllables
corroborate, authenticate