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)



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