What is Attest?

Legal Definition
To testify or confirm that something is true, genuine, or authentic. See attestation.
Illustrative case law
See, e.g. Keely v. Moore, 196 U.S. 38 (1904).
See also
Legal Definition
To witness the execution of a written instrument, at the request of him who makes it, and subscribe the same as a witness. White v. Magarahan, 87 Ga. 217, 13 S. 14 509; Logwood v. Hussey, 60 Ala. 424; Arrington v. Arrington, 122 Ala. 510, 26 South. 152. This is also the technical word by which, in the practice in many of the states, a certifying officer gives assurance of the genuineness and correctness ot a copy. An "attested" copy of a document is one which has been examined and compared with the original, with a certificate or memorandum of its correctness, signed by the persons who have examined it. Goss, etc., Co. v. People, 4 111. App. 515; Donaldson v. Wood, 22 Wend. (N. Y.) 400; Gerner v. Mosher, 58 Neb. 135, 78 N. W. 384, 46 L. It. A. 244.
-- Black's Law Dictionary
Legal Definition
A witness; to witness.
-- Ballentine's Law Dictionary