spectator — a weekly periodical (1711–12, 1714) issued by Joseph Addison and Richard Steele.
testimony — Law. the statement or declaration of a witness under oath or affirmation, usually in court.
attest — To attest something or attest to something means to say, show, or prove that it is true.
attestor — to bear witness to; certify; declare to be correct, true, or genuine; declare the truth of, in words or writing, especially affirm in an official capacity: to attest the truth of a statement.
beholder — The beholder of something is the person who is looking at it.
deponent — (of a verb, esp in Latin) having the inflectional endings of a passive verb but the meaning of an active verb
looker-on — a person who looks on; onlooker; witness; spectator.
watcher — a person who watches or who keeps watch.
corroborator — to make more certain; confirm: He corroborated my account of the accident.
witness — to see, hear, or know by personal presence and perception: to witness an accident.
attester — to bear witness to; certify; declare to be correct, true, or genuine; declare the truth of, in words or writing, especially affirm in an official capacity: to attest the truth of a statement.
seer — a unit of weight in India, varying in value but usually 1/40 of a maund: the government ser is divided into 80 tolas of 180 English grains and equals nearly 2 pounds 1 ounce avoirdupois (950 grams).