Pronunciation: (härd'pan"), [key]
1. any layer of firm detrital matter, as of clay, underlying soft soil. Cf. caliche, duricrust.
2. hard, unbroken ground.
3. the fundamental or basic aspect of anything; solid foundation; underlying reality: the hardpan of mathematical theory.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.