The Collaborative International Dictionary of English v.0.48:

Grit \Grit\ (gr[i^]t), v. i.
   To give forth a grating sound, as sand under the feet; to
   grate; to grind.
   [1913 Webster]

         The sanded floor that grits beneath the tread.
                                                  --Goldsmith.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Grit \Grit\, v. t. [imp. & p. p. Gritted; p. pr. & vb. n.
   Gritting.]
   To grind; to rub harshly together; to grate; as, to grit the
   teeth. [Collog.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Grit \Grit\, n. [OE, greet, greot, sand, gravel, AS. gre['o]t
   grit, sant, dust; akin to OS griott, OFries. gret gravel,
   OHG. grioz, G. griess, Icel. grj[=o]t, and to E. groats,
   grout. See Groats, Grout, and cf. Grail gravel.]
   1. Sand or gravel; rough, hard particles.
      [1913 Webster]

   2. The coarse part of meal.
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   3. pl. Grain, esp. oats or wheat, hulled and coarsely ground;
      in high milling, fragments of cracked wheat smaller than
      groats.
      [1913 Webster]

   4. (Geol.) A hard, coarse-grained siliceous sandstone; as,
      millstone grit; -- called also gritrock and gritstone.
      The name is also applied to a finer sharp-grained
      sandstone; as, grindstone grit.
      [1913 Webster]

   5. Structure, as adapted to grind or sharpen; as, a hone of
      good grit.
      [1913 Webster]

   6. Firmness of mind; invincible spirit; unyielding courage;
      fortitude. --C. Reade. --E. P. Whipple.
      [1913 Webster]

WordNet (r) 3.0 (2006):

grit
    n 1: a hard coarse-grained siliceous sandstone [syn: grit,
         gritrock, gritstone]
    2: fortitude and determination; "he didn't have the guts to try
       it" [syn: backbone, grit, guts, moxie, sand,
       gumption]
    v 1: cover with a grit; "grit roads"
    2: clench together; "grit one's teeth"

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "grit":
   air pollution, attritus, backbone, bottle, bottom, bran, bravery,
   breccia, chafe, chutzpah, cosmic dust, courage, courageousness,
   crumb, crumble, dauntlessness, debris, determination, detritus,
   doughtiness, dust, dust ball, efflorescence, exacerbate, fallout,
   farina, fearlessness, filings, firmness, flour, fortitude, fret,
   gall, gameness, grain, granule, granulet, grate, grate on, gravel,
   grits, groats, guts, gutsiness, guttiness, hardihood, hardiness,
   heart, heart of oak, intestinal fortitude, intrepidity,
   intrepidness, irritate, kittens, lint, meal, mettle,
   mettlesomeness, moxie, nerve, pith, pluck, pluckiness, powder,
   provoke, pussies, rasp, raspings, resoluteness, resolution,
   resolve, sand, sawdust, set on edge, shingle, smut, soot, spirit,
   spunk, spunkiness, stalwartness, stamina, starch, staunchness,
   stout heart, tenacity, toughness, true grit, valor