The Collaborative International Dictionary of English v.0.48:

icecap \ice"cap`\ ([imac]s"k[a^]p`) n.
   a mass of ice and snow that permanently covers a large area
   of land (e.g., the polar regions or a mountain peak).
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

icecap
    n 1: a mass of ice and snow that permanently covers a large area
         of land (e.g., the polar regions or a mountain peak) [syn:
         icecap, ice cap]