Attest definition (verb)

1. To attest is to swear under oath that something is true or genuine.

2. To attest is to bear witness to the truth.

3. In legal cases, there are times when a document needs to be signed in front of a witness who can attest that they observed the person signing the document, so it is indeed that person’s signature.

4. In the art world, a certificate may come with a painting that attests that the painting is in fact genuine.