To hit something or someone very hard.
He whop him on the head with a bat.
彼はバットで彼の頭を叩いた。
To easily win against someone.
She whop her opponent in the chess tournament.
彼女はチェスのトーナメントで対戦相手に勝った。
An exclamation showing surprise.
Whop, I didn't see you there!
ああ、私はそこであなたに会わなかった!