The Collaborative International Dictionary of English v.0.48:

Glacial \Gla"cial\, a. [L. glacialis, from glacies ice: cf. F.
   glacial.]
   1. Pertaining to ice or to its action; consisting of ice;
      frozen; icy; esp., pertaining to glaciers; as, glacial
      phenomena. --Lyell.
      [1913 Webster]

   2. (Chem.) Resembling ice; having the appearance and
      consistency of ice; -- said of certain solid compounds;
      as, glacial phosphoric or acetic acids.
      [1913 Webster]

   Glacial acid (Chem.), an acid of such strength or purity as
      to crystallize at an ordinary temperature, in an icelike
      form; as acetic or carbolic acid.

   Glacial drift (Geol.), earth and rocks which have been
      transported by moving ice, land ice, or icebergs; bowlder
      drift.

   Glacial epoch or Glacial period (Geol.), a period during
      which the climate of the modern temperate regions was
      polar, and ice covered large portions of the northern
      hemisphere to the mountain tops.

   Glacial theory or Glacial hypothesis. (Geol.) See
      Glacier theory, under Glacier.
      [1913 Webster]

WordNet (r) 3.0 (2006):

glacial period
    n 1: any period of time during which glaciers covered a large
         part of the earth's surface; "the most recent ice age was
         during the Pleistocene" [syn: ice age, glacial period,
         glacial epoch]