If you smack someone, you hit them with your hand.

If you smack something somewhere, you put it or throw it there so that it makes a loud, sharp noise.

If one thing smacks of another thing that you consider bad, it reminds you of it or is like it.

Something that is smack in a particular place is exactly in that place.

Smack is heroin.

If you smack your lips, you open and close your mouth noisily, especially before or after eating, to show that you are eager to eat or enjoyed eating.