What's the difference between i.e. and e.g.?
c.1300, "to strike, strike the hands together," possibly imitative of the sound of hitting. The sense of "exchange, barter, trade" is first recorded 1590s, possibly from the practice of slapping hands together as a sign of agreement in bargaining. Related: Swapped; swapping. The noun in this sense is attested from 1620s.