Source : Webster's Revised Unabridged Dictionary (1913)

Drumlin \Drum"lin\, n. [Gael. druim the ridge of a hill.]
   (Geol.)
   A hill of compact, unstratified, glacial drift or till,
   usually elongate or oval, with the larger axis parallel to
   the former local glacial motion.

Source : WordNet®

drumlin
     n : a mound of glacial drift