The Collaborative International Dictionary of English v.0.48:

Crag \Crag\ (kr[a^]g), n. [W. craig; akin to Gael. creag, Corn.
   karak, Armor. karrek.]
   1. A steep, rugged rock; a rough, broken cliff, or point of a
      rock, on a ledge.
      [1913 Webster]

            From crag to crag the signal flew.    --Sir W.
                                                  Scott.
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   2. (Geol.) A partially compacted bed of gravel mixed with
      shells, of the Tertiary age.
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The Collaborative International Dictionary of English v.0.48:

Crag \Crag\, n. [A form of craw: cf. D. kraag neck, collar, G.
   kragen. See Craw.]
   1. The neck or throat [Obs.]
      [1913 Webster]

            And bear the crag so stiff and so state. --Spenser.
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   2. The neck piece or scrag of mutton. --Johnson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

crag
    n 1: a steep rugged rock or cliff

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "crag":
   aa, abyssal rock, basalt, bedrock, block lava, bluff, brash,
   breccia, cliff, cog, comb, conglomerate, druid stone, escarpment,
   face, fang, festooned pahoehoe, gneiss, granite, harrow,
   igneous rock, jag, lava, limestone, living rock, magma, mantlerock,
   metamorphic rock, monolith, pahoehoe, palisade, palisades, peak,
   pecten, pillow lava, porphyry, precipice, projection,
   pudding stone, rake, ratchet, regolith, rock, ropy lava, rubble,
   rubblestone, sandstone, sarsen, sawtooth, scar, scarp, schist,
   scoria, scree, sedimentary rock, shelly pahoehoe, snag, snaggle,
   spire, sprocket, spur, steep, steeple, stone, talus, tooth, tor,
   tufa, tuff, wall