1. intransitive verb stop talking: to be quiet or stop talking ( informal )
I shut up before saying something I would regret.
2. transitive verb silence somebody: to cause somebody to be quiet or stop talking ( informal )
She shot me a look that shut me up instantly.
3. transitive verb confine somebody: to confine or imprison somebody or something
She shut the dog up in the pen.
4. transitive verb close something: to close or prevent entrance to something
The building is all shut up.
http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861735240
1. (transitive) To close (a building) so that no one can enter.
2. (transitive) To terminate (a business).
3. (transitive) To enclose (a person, animal or thing) in a room or other place so that it cannot leave.
4. (transitive) To put (an object) in a secure enclosed place.
5. (transitive) To stop (a person) from talking or (a person or thing) making noise.
6. (intransitive) Of a person, to stop talking or (of a person or thing) making noise.
You are talking so loud that I can't hear the music — would you mind shutting up?
7. (intransitive, slang, used only in the imperative) I don't believe it!, no way!
Usage notes
When used in the imperative to tell someone to be quiet or to stop making a noise, this expression is considered forceful or impolite. A neutral alternative is "be quiet".
Synonyms
* (close (a building)): close off, seal up
* (terminate (a business)): end, terminate, wind up
* (enclose (a person, animal or thing) in a room so that it cannot leave): lock in, seal in
* (put (an object) in a secure enclosed place): lock up, stash, stash away
* (to stop (a person) from talking or (a person or thing) making noise): hush, quieten, shush, silence
* (to stop talking or making noise): be quiet, be silent, fall silent, hush, quieten down, shush; (in the imperative): be quiet!, can it!, hush!, put a sock in it!, quiet!, sh!, shush!, shut it!, shut your face! (impolite), silence!, st!
* (I don't believe it): never!, no!, no way!, you don't say!
http://en.wiktionary.org/wiki/shut_up?rdfrom=Shut_up&redirect=no
From the Oxford English Dictionary, two early uses:
1826
"Let them answer the question, or shut up their mouths upon this subject."
1852
"Well, his mouth's shut up at last."
http://www.phrases.org.uk/bulletin_board/42/messages/125.html
1. Imprison, confine, enclose, as in The dog was shut up in the cellar for the night, or She shut up her memories and never talked about the past. [c. 1400]
2. Close completely, as in The windows were shut up tightly so no rain came in. [Early 1500s] This usage also occurs in shut up shop, meaning "close the premises of a business," as in It's late, let's shut up shop now. [Late 1500s] Also see close up, def. 3.
3. Cause someone to stop speaking, silence someone, as in It's time someone shut him up. [Early 1800s]
4. Stop speaking, as in I've told you what I think and now I'll shut up. This usage also occurs as a rather rude imperative, as in Shut up! You've said enough. [First half of 1800s]
http://www.answers.com/Shut%20up
Synonyms: pent (adj), shut up(p) (adj), be quiet (v), belt up (v), button up (v), clam up (v), close up (v), dummy up (v), hush (v), hush up (v), keep mum (v), lock (v), lock away (v), lock in (v), lock up (v), put away (v), quieten (v), shut away (v), silence (v), still (v).
Expressions using "shut up": hold your jaw! shut up your mouth! ♦ shut up shop ♦ shut up your mouth! ♦ To shut up.