The Collaborative International Dictionary of English v.0.48:

Crevasse \Cre`vasse"\ (kr?`v?s"), n. [F. See Crevice.]
   1. A deep crevice or fissure, as in embankment; one of the
      clefts or fissure by which the mass of a glacier is
      divided.
      [1913 Webster]

   2. A breach in the levee or embankment of a river, caused by
      the pressure of the water, as on the lower Mississippi.
      [U.S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

crevasse
    n 1: a deep fissure