Attest

google

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early 16th century: from French attester, from Latin attestari, from ad- ‘to’ + testari ‘to witness’ (from testis ‘a witness’).

wiktionary

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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”).

etymonline

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attest (v.)

1590s, "bear witness to, officially confirm; give proof or evidence of," from French attester (Old French atester, 13c.) "affirm, bear witness to," from Latin attestari "confirm, prove," literally "bear witness to," from assimilated form of ad "to" (see ad-) + testari "bear witness," from testis "witness" (see testament). Related: Attested; attesting.