from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
ATTESTING WITNESS. One who, upon being required by the parties to an
instrument, signs his name to it to prove it, and for the purpose of
identification.
2. The witness must be desired by the parties to attest it, for unless
this be done, he will not be an attesting witness, although he may have seen
the parties execute it. 3 Campb. 232. See Competent witness; Credible
witness; Disinterested witness; Respectable witness; Subscribing witness;
and Witness; Witness instrumentary; 5 Watts, 399; 3 Bin. 194.