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late 14c., from Old French confesser (transitive and intransitive), from Vulgar Latin *confessare, from Latin confess-, past participle stem of confiteri "to acknowledge," from com- "together" (see com-) + fateri "to admit," akin to fari "speak" (see fame (n.)).
Its original religious sense was of one who avows his religion in spite of persecution or danger but does not suffer martyrdom. Old French confesser thus had a figurative sense of "to harm, hurt, make suffer." Related: Confessed; confessing. An Old English word for it was andettan.