The Collaborative International Dictionary of English v.0.48:

Attestation \At`tes*ta"tion\, n. [L. attestatio: cf. F.
   attestation.]
   The act of attesting; testimony; witness; a solemn or
   official declaration, verbal or written, in support of a
   fact; evidence. The truth appears from the attestation of
   witnesses, or of the proper officer. The subscription of a
   name to a writing as a witness, is an attestation.
   [1913 Webster]

WordNet (r) 3.0 (2006):

attestation
    n 1: the action of bearing witness
    2: the evidence by which something is attested