verb
1.
to testify usually formally and in writing to the truth or genuineness of something
certify a student's college transcript
Synonyms: attest, vouch, witness
Related Word: assert, aver, avouch, avow, profess
2.
Synonyms: warrant 2, guarantee, guaranty
3.
Synonyms: approve 2, accredit, endorse, OK ( or okay), sanction
Related Word: authorize, commission, license
Contrasted words: antagonize, counter, oppose