"large or impressive person or thing," 1781, agent noun from slap (v.). Also see whopper.
late 15c., "strike with the open hand," from slap (n.). As an adverb, 1670s, "suddenly;" 1829, "directly." Related: Slapped; slapping.
1767, "uncommonly large thing," originally and especially an audacious lie, formed as if from whop (v.) "to beat, overcome." Whopping "large, big, impressive" is attested by 1620s.
updated on April 03, 2014