swat v.

c. 1200, "to strike, strike the hands together," of uncertain origin, possibly imitative of the sound of hitting or slapping. The sense of "to exchange, barter, trade" is first recorded 1590s, possibly from the notion of slapping hands together as a sign of agreement in bargaining (as in strike a bargain). Related: Swapped; swapping. The noun in this sense is attested from 1620s; earlier "a striking, an act of striking" (mid-13c.). Swap-meet attested from 1968, American English.

in reference to a bit of wire mesh on a handle, 1917, from fly (n.) + agent noun from swat (v.). Simple swatter was used in this sense by 1906. Other older names for similar implements were fly-duster (1860), fly-whisk (1836), fly-brush (1823), fly-fan (1821), fly-flap (mid-15c., glossing Latin muscarium).

"instrument for swatting flies," 1906, agent noun from swat (v.).