from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A substratum.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The layer, or stratum, of earth on which the soil rests; the subsoil.
from the GNU version of the Collaborative International Dictionary of English
- n. The layer, or stratum, of earth on which the mold, or soil, rests; subsoil.
from The Century Dictionary and Cyclopedia
- n. A substratum; an underlying stratum; the stratum lying immediately beneath, or forming the lower portion of the one designated: not often used except figuratively.
under- + stratum (Wiktionary)