The Collaborative International Dictionary of English v.0.48:

Abrasion \Ab*ra"sion\, n. [L. abrasio, fr. abradere. See
   Abrade.]
   1. The act of abrading, wearing, or rubbing off; the wearing
      away by friction; as, the abrasion of coins.
      [1913 Webster]

   2. The substance rubbed off. --Berkeley.
      [1913 Webster]

   3. (Med.)
      (a) A superficial excoriation of skin or mucous membranes.
          --AS
      (b) Erosion of the tooth substance --AS
          [1913 Webster]

WordNet (r) 3.0 (2006):

abrasion
    n 1: an abraded area where the skin is torn or worn off [syn:
         abrasion, scratch, scrape, excoriation]
    2: erosion by friction [syn: abrasion, attrition,
       corrasion, detrition]
    3: the wearing down of rock particles by friction due to water
       or wind or ice [syn: grinding, abrasion, attrition,
       detrition]

Moby Thesaurus II by Grady Ward, 1.0:

102 Moby Thesaurus words for "abrasion":
   ablation, abrasive, abstraction, atomization, attrition, beating,
   blemish, break, brecciation, buffing, burn, burnishing, chafe,
   chafing, check, chip, comminution, concussion, crack, crackle,
   craze, crumbling, crushing, cut, deduction, detrition,
   disintegration, dressing, erasure, erosion, filing, flash burn,
   fracture, fragmentation, fray, frazzle, fretting, gall, galling,
   gash, granulation, granulization, grating, grazing, grinding, hurt,
   incision, injury, laceration, lesion, levigation, limation,
   mashing, mortal wound, mutilation, polishing, pounding, powdering,
   puncture, purification, rasping, refinement, removal, rent, rip,
   rubbing away, run, rupture, sandblasting, sanding, scald, scorch,
   scouring, scrape, scraping, scratch, scratching, scrub, scrubbing,
   scuff, second-degree burn, shining, shredding, slash, smashing,
   smoothing, sore, stab, stab wound, subduction, sublation,
   subtraction, taking away, tear, third-degree burn, trauma,
   trituration, wear, wearing away, wound, wounds immedicable,
   wrench