from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The lowest possible level or absolute bottom: Prices have hit rock bottom.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The very lowest possible level.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the absolute bottom
The sub-stratum of the sea-floor, below the sand. (Wiktionary)