To assure or make certain (of); give certain information to; tell positively: applied to persons, and followed by of before the thing told about, or by that before a verb and its nominative: as, I certified you of the fact.To give certain information of; make clear, definite, or certain; vouch for: applied to things.To testify to or vouch for in writing; make a declaration of in writing under hand, or hand and seal; make known or establish as a fact.To testify; declare the truth; make a certification or certificate.