from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Of less than audible frequency.
- adj. Having a speed less than that of sound in a designated medium.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. having a frequency too low to be audible
- adj. less than the speed of sound (in the same medium, and at the same temperature and pressure)
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. (of speed) less than that of sound in a designated medium
Sorry, no etymologies found.