from The American Heritage® Dictionary of the English Language, 4th Edition
- intransitive v. To spar with an imaginary opponent, as for exercise or training purposes.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A diorama
- v. To practice moves without an actual opponent, often in front of a mirror.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- v. go through boxing motions without an opponent
shadow + box (Wiktionary)