1. To stop speaking or be silent. Very rude when used as an imperative. Would you shut up already? I'm sick of hearing you complain. I decided to shut up before I made things any worse.

2. To cause or compel someone to stop speaking or be silent. In this usage, a noun or pronoun can be used between "shut" and "up." The mobsters threatened the witness to try and shut him up. The exasperated dad was trying to find some way of shutting up the kids while he made a phone call.

3. To imprison or lock someone into some place; to confine someone. In this usage, a noun or pronoun can be used between "shut" and "up." They shut the criminal up in a tiny windowless cell as punishment for attacking another inmate. I feel so trapped, like I've been shut up in the house all day.