from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Not allowing the passage of x-rays or other radiation.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. impenetrable to X-rays and other radiation
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. not transparent to X-rays or other forms of radiation
Sorry, no etymologies found.