Other forms: whopping
To whop is to strike somebody with a heavy blow. Whop him one, whopped the ball, got whopped.
It is informal and dialectal, and the sound of the word is the blow. It also means to defeat soundly. Note whopping, meaning enormous, which comes from the same root and is far commoner — a whopping great thing is one that lands with force. The word is probably imitative.
1verbwhopTo strike somebody with a heavy blow.
“He whopped the thief across the back with his umbrella and shouted for help.”
whop is a heavy striking.
Middle English whappen is a variant of wappen, to strike, probably imitative of the sound.
Middle English
whappen
English, today
whop
Built from
From Middle English whappen, a variant of wappen (“to strike; fling; shoot; stun”), probably of imitative origin. Compare Old Norse vappa (“to waddle”).
Etymology from Wiktionary, CC BY-SA