An Etymological Dictionary of Astronomy and Astrophysics

To acknowledge or avow (a fault, crime, misdeed, weakness, etc.) by way of revelation (Dictionary.com).

Etymology (EN): M.E. confessen, from Old French confesser (transitive and intransitive), from Vulgar Latin *confessare, from Latin confess-, past participle stem of confiteri “to acknowledge,” from assimilated form of com “together” (see com-) + fateri “to admit,” akin to fari “speak,” from PIE root *bha- (2) “to speak, tell, say.”

Etymology (PE): Xastuyidan, infinitive from xastu, → confessor.