Underclay
Pronunciation : Un"der*clay`
Part of Speech : n.
Definition : Defn: A stratum of clay lying beneath a coal bed, often containing the roots of coal plants, especially the Stigmaria.
(Geol.)
Source : Webster's Unabridged Dictionary, 1913
Merriam-Webster's Everyday Language Reference Set: Includes: The Merriam-Webster Dictionary, The Merriam-Webster Thesaurus, and The Merriam-Webster Vocabulary Builder