Synonyms for Certify (same or very similar meaning)
WordNet sense 1 (guarantee as meeting a certain standard):
endorse, indorseWordNet sense 2 (authorize officially):
license, licenceWordNet sense 3 (provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes):
attest, demonstrate, evidence, manifestFrom the ODE community, based on WordNetadd/edit