The Collaborative International Dictionary of English v.0.48:

Grate \Grate\, v. t. [imp. & p. p. Grated; p. pr. & vb. n.
   Grating.]
   To furnish with grates; to protect with a grating or
   crossbars; as, to grate a window.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Grating \Grat"ing\, n. [See 2d Grate.]
   1. A partition, covering, or frame of parallel or cross bars;
      a latticework resembling a window grate; as, the grating
      of a prison or convent.
      [1913 Webster]

   2. (Optics) A system of close equidistant parallel lines or
      bars, esp. lines ruled on a polished surface, used for
      producing spectra by diffraction; -- called also
      diffraction grating.

   Note: Gratings have been made with over 40,000 such lines to
         the inch, but those with a somewhat smaller number give
         the best definition. They are used, e. g., to produce
         monochromatic light for use in optical instruments such
         as spectrophotometers.
         [Webster 1913 Suppl.]

   3. pl. (Naut.) The strong wooden lattice used to cover a
      hatch, admitting light and air; also, a movable Lattice
      used for the flooring of boats.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Grating \Grat"ing\, a. [See Grate to rub harshy.]
   That grates; making a harsh sound; harsh. -- Grat"ing*ly,
   adv.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Grating \Grat"ing\, n.
   A harsh sound caused by attrition.
   [1913 Webster]

WordNet (r) 3.0 (2006):

grating
    adj 1: unpleasantly harsh or grating in sound; "a gravelly
           voice" [syn: grating, gravelly, rasping, raspy,
           rough, scratchy]
    n 1: a barrier that has parallel or crossed bars blocking a
         passage but admitting air [syn: grate, grating]
    2: a frame of iron bars to hold a fire [syn: grate, grating]
    3: optical device consisting of a surface with many parallel
       grooves in it; disperses a beam of light (or other
       electromagnetic radiation) into its wavelengths to produce
       its spectrum [syn: diffraction grating, grating]

Moby Thesaurus II by Grady Ward, 1.0:

208 Moby Thesaurus words for "grating":
   abrasion, absonant, ajar, andiron, annoying, antagonistic,
   antipathetic, arabesque, at cross-purposes, at loggerheads,
   at odds, at variance, at war, atomization, atonal, attrition,
   basketry, basketwork, beating, bolter, brecciation, cacophonous,
   cancellation, chafing, chain, clashing, coal tongs, colander,
   comminution, conflicting, confused, contradictory, contrary,
   cracked, crane, cranky, creaking, croaking, crook, cross,
   cross-hatching, crossing-out, crumbling, crushing, damper,
   detrition, diaphonic, differing, disaccordant, disagreeable,
   disagreeing, disconsonant, discordant, discrepant, disharmonic,
   disharmonious, disintegration, disproportionate, dissident,
   dissonant, divergent, dry, filigree, fire hook, fire tongs,
   firedog, flat, fragmentation, fret, fretting, fretwork, galling,
   granulation, granulization, grate, grid, griddle, gridiron, grill,
   grille, griller, grillwork, grinding, gritty, hachure, harsh,
   hatching, hoarse, hostile, immelodious, immiscible, inaccordant,
   incompatible, inharmonic, inharmonious, interlacement,
   intertexture, intertwinement, irksome, irritant, irritating,
   irritative, jangling, jangly, jarring, jostling, lace, lacery,
   lacework, lacing, lattice, latticework, levigation, lifter,
   mashing, mesh, meshes, meshwork, musicless, negative,
   nerve-jangling, nerve-racking, nerve-rending, nerve-shaking,
   nerve-trying, net, netting, network, nonmelodious, off, off-key,
   off-tone, offensive, out of accord, out of pitch, out of tone,
   out of tune, out of whack, piercing, plexure, plexus, poker,
   pothook, pounding, powdering, raddle, rasping, raspy, raucous,
   repugnant, reticle, reticulation, reticule, reticulum, riddle,
   rough, salamander, scraping, scrapy, scratching, scratchy,
   screeching, screen, screening, sharp, shredding, shrill, sieve,
   sifter, smashing, sorter, sour, spit, squawking, squeaky, stinging,
   strident, stridulous, texture, tissue, tongs, tracery, trellis,
   trelliswork, tripod, trituration, trivet, tuneless, turnspit,
   uncongenial, unharmonious, unmelodious, unmusical, untunable,
   untuned, untuneful, variant, vexatious, warring, wattle, weave,
   weaving, web, webbing, webwork, weft, wicker, wickerwork