certify, attest, witness, vouch mean to testify to the truth or genuineness of something. certify usually applies to a written statement, especially one carrying a signature or seal <certified that the candidate had met all requirements>. attest applies to oral or written testimony usually from experts or witnesses <attested to the authenticity of the document>. witness applies to the subscribing of one’s own name to a document as evidence of its genuineness <witnessed the signing of the will>.vouch applies to one who testifies as a competent authority or a reliable person <willing to vouch for her integrity>