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c.1200, "vows taken upon entering a religious order," from Old French profession (12c.), from Latin professionem (nominative professio) "public declaration," from past participle stem of profiteri "declare openly" (see profess). Meaning "any solemn declaration" is from mid-14c. Meaning "occupation one professes to be skilled in" is from early 15c.; meaning "body of persons engaged in some occupation" is from 1610; as a euphemism for "prostitution" (e.g. oldest profession) it is recorded from 1888.