massif

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

• noun A large mountain mass or compact group of connected mountains forming an independent portion of a range.
• noun A large section or block of the earth's crust that is more rigid than the surrounding rock and has been moved or displaced as a unit.

from The Century Dictionary.

• noun A central mountain-mass; the dominant part of a range of mountains; a part of a range which appears, from the position of the depressions by which it is more or less isolated, to form an independent whole; also, an orographic block or fault-block (German scholle); a band or zone of rocks raised or depressed between two largely developed parallel faults.

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

• noun (Geol.) A block of the earth's crust bounded by faults and shifted to form peaks of a mountain range.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A principal mountain mass.
• noun A block of the earth's crust bounded by faults or flexures and displaced as a unit without internal change; normally consists of gneisses and schists

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a block of the earth's crust bounded by faults and shifted to form peaks of a mountain range