What's the difference between i.e. and e.g.?
early 14c., "to take a vow" (in a religious order), a back-formation from profession or else from Old French profes, from Medieval Latin professus "avowed," literally "having declared publicly," past participle of Latin profiteri "declare openly, testify voluntarily, acknowledge, make public statement of," from pro- "forth" (see pro-) + fateri (past participle fassus) "acknowledge, confess," akin to fari "speak" (see fame (n.)). Meaning "declare openly" first recorded 1520s, "a direct borrowing of the sense from Latin" [Barnhart]. Related: Professed; professing.