whopper (n.)

"to beat, strike," mid-15c., of imitative origin. Compare Welsh chwap "a stroke," also of imitative origin; also see wap. Related: Whopped; whopping.

"large or impressive person or thing," attested by 1781 in glossaries of Northern dialect, agent noun from slap (v.). Compare whopper. By 1886 as "implement for slapping."

1794, "uncommonly large thing," agent noun from smash (v.); compare whopper, slapper, etc. By 1822 as "machine which crushes;" by 1829 as "a heavy blow."