The Collaborative International Dictionary of English v.0.48:

Canon \Ca*[~n]on"\ (k[aum]*ny[-o]n"; anglicized k[a^]n"y[u^]n),
   n. [Sp., a tube or hollow, fr. ca[~n]a reed, fr. L. canna.
   See Cane.]
   A deep gorge, ravine, or gulch, between high and steep banks,
   worn by water courses. [Mexico & Western U. S.] [Also spelled
   canyon.]
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Canyon \Can"yon\, n.
   The English form of the Spanish word Ca[~n]on.
   [1913 Webster]

WordNet (r) 3.0 (2006):

canyon
    n 1: a ravine formed by a river in an area with little rainfall
         [syn: canyon, canon]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "canyon":
   abysm, abyss, arroyo, box canyon, breach, break, cavity, chap,
   chasm, check, chimney, chink, cleft, cleuch, clough, col, coulee,
   couloir, crack, cranny, crevasse, crevice, cut, cwm, defile, dell,
   dike, ditch, donga, draw, excavation, fault, fissure, flaw, flume,
   fracture, furrow, gap, gape, gash, gill, gorge, groove, gulch,
   gulf, gully, hole, incision, joint, kloof, leak, moat, notch,
   nullah, opening, pass, passage, ravine, rent, rift, rime, rupture,
   scissure, seam, slit, slot, split, trench, valley, void, wadi