sérac

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A large pointed mass of ice in a glacier isolated by intersecting crevasses.

from The Century Dictionary.

• noun A name current in the Swiss Alps, and commonly used by writers in English on the glaciers of that region, to designate the grand cuboidal or parallelepipedal masses into which the névé breaks in passing down a steep incline, in consequence of the intersection of the transverse and longitudinal crevasses to which the descent gives rise.

from the GNU version of the Collaborative International Dictionary of English.

• noun A pinnacle of ice among the crevasses of a glacier; also, one of the blocks into which a glacier breaks on a steep grade.