Source : Webster's Revised Unabridged Dictionary (1913)

Peneplain \Pe"ne*plain`\, n. [L. paene, pene, almost + E.
   plain.] (Phys. Geog.)
   A land surface reduced by erosion to the general condition of
   a plain, but not wholly devoid of hills; a base-level plain.

Source : WordNet®

peneplain
     n : a more or less level land surface representing and advanced
         stage of erosion undisturbed by crustal movements [syn: {peneplane}]