"attested by certificate," 1610s, past-participle adjective from certify. Certified public accountant attested from 1896; certified mail from 1955.
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certify v.
mid-14c., "to declare the truth of," also "to vouch for or confirm" (an official record, etc.), from Old French certefiier "make certain, witness the truth of" (12c.), from Late Latin certificare "to certify, to make certain," from Latin certus "fixed, sure" (see certain) + root of facere "to make, do" (from PIE root *dhe- "to set, put"). Also used in Middle English in broader senses of "inform, give notice to; instruct, to direct; to designate." Related: Certified; certifying.