The Oxford Thesaurus An A-Z Dictionary of Synonyms - witness n.

1) observer, onlooker, spectator, viewer, eyewitness, bystander, watcher, Rare earwitness: Were you a witness to what took place here? 2 deponent, testifier, corroborating witness, corroborator: The defence will call its witnesses today. 3) bear witness (to or of) . testify (to) , attest (to) , be or give or provide or furnish or constitute evidence or proof or testimony (of or to) , verify, confirm, corroborate, show, prove: The bent poker bears witness to the violence of the attack. --v. 4) see, observe, watch, look on or at, view, behold, mark, note, notice, take in, Colloq spot, catch: I did witness the way they looked at each other. 5) countersign, sign, certify, endorse, substantiate, document, certificate: Would you mind witnessing our signatures, Miss Cabot? 6 See 3, above.