—v.t. 1. to attest as certain; give reliable information of; confirm: He certified the truth of his claim. 2. to testify to or vouch for in writing: The medical examiner will certify his findings to the court. 3. to guarantee; endorse reliably: to certify a document with an official seal. 4. to guarantee (a check) by writing on its face that the account against which it is drawn has sufficient funds to pay it.
5. to award a certificate to (a person) attesting to the completion of a course of study or the passing of a qualifying examination.
6. to declare legally insane and committable to a mental institution.
7. Archaic.to assure or inform with certainty.
—v.i. to give assurance; testify; vouch for the validity of something (usually fol. by to).