wal ‧ lop /ˈwɒləp $ ˈwɑː-/ BrE AmE verb [transitive]
[ Date: 1300-1400 ; Language: Old North French ; Origin: waloper , from Old French galoper ; ⇨ ↑ gallop 1 ]
informal to hit someone or something very hard, especially with your hand
—wallop noun [singular]