from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The level layer of rock or earth upon which the foundation of a road or railway is laid.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The layer of native soil on which the foundation of a road is laid
from The Century Dictionary and Cyclopedia
- n. A grade of the second rank in zoölogical classification; a prime division of a grade: used like subclass, suborder, etc. See grade, 3.
sub- + grade (Wiktionary)