from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Not penetrable by audible sound.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Describing something that does not allow sound through.
- v. To make resistant to transmitting sound.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- v. insulate against noise
- adj. impervious to, or not penetrable by, sound
sound + -proof (Wiktionary)