Source : Webster's Revised Unabridged Dictionary (1913)

Glacier \Gla"cier\, n. [F. glacier, fr. glace ice, L. glacies.]
   An immense field or stream of ice, formed in the region of
   perpetual snow, and moving slowly down a mountain slope or
   valley, as in the Alps, or over an extended area, as in
   Greenland.

   Note: The mass of compacted snow forming the upper part of a
         glacier is called the firn, or n['e]v['e]; the glacier
         proper consist of solid ice, deeply crevassed where
         broken up by irregularities in the slope or direction
         of its path. A glacier usually carries with it
         accumulations of stones and dirt called moraines, which
         are designated, according to their position, as
         lateral, medial, or terminal (see {Moraine}). The
         common rate of flow of the Alpine glaciers is from ten
         to twenty inches per day in summer, and about half that
         in winter.

   {Glacier theory} (Geol.), the theory that large parts of the
      frigid and temperate zones were covered with ice during
      the glacial, or ice, period, and that, by the agency of
      this ice, the loose materials on the earth's surface,
      called drift or diluvium, were transported and
      accumulated.

Source : WordNet®

glacier
     n : a slowly moving mass of ice