to hit sb with your open hand, especially as a punishment 用巴掌打；掴
I think it’s wrong to smack children.
我觉得打孩子不对。
[T] ~ sth + adv./prep.to put sth somewhere with a lot of force so that it makes a loud noise 啪的一声使劲放（或扔、甩等） SYN bang
She smacked her hand down on to the table.
她啪地一拍桌子。
He smacked a fist into the palm of his hand.
他用拳头啪地猛击一下手掌。
[I] + adv./prep.to hit against sth with a lot of force 使劲碰（或撞） SYN crash
Two players accidentally smacked into each other.
两名运动员不巧撞在了一起。