Definition of subgrade in English:

subgrade

noun

  • 1A subsidiary or subordinate grade; a secondary gradation; a grade within a grade.

  • 2In the construction of roads and other flat load-bearing surfaces: the layer (typically the prepared natural ground) lying immediately beneath the foundations.

Origin

Late 18th century. From sub- + grade.

Pronunciation

subgrade

/ˈsʌbɡreɪd/