Meaning

verb provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes

verb authenticate, affirm to be true, genuine, or correct, as in an official capacity

verb give testimony in a court of law

originPIE word *tréyes Borrowed from Middle French attester, from Latin attestor (“to witness to, bear witness”), from at-, combining form of ad (“to”) + testor (“to bear witness”), from testis (“a witness”).

Etymology from Wiktionary, CC BY-SA 3.0