The Collaborative International Dictionary of English v.0.48:

Ablation \Ab*la"tion\, n. [L. ablatio, fr. ablatus p. p. of
   auferre to carry away; ab + latus, p. p. of ferre carry: cf.
   F. ablation. See Tolerate.]
   1. A carrying or taking away; removal. --Jer. Taylor.
      [1913 Webster]

   2. (Med.) Extirpation. --Dunglison. AS
      [1913 Webster]

   3. (Med.) Removing or destroying of a body tissue, especially
      by a surgical procedure. --Dorland.
      [AS]

   4. (Geol.) Wearing away; superficial waste, as of glacial ice
      or snow. --Tyndall.
      [1913 Webster]

   5. (Aerospace) Wearing away of the outer layers of a
      protective shield or surface by the heat and aerodynamic
      forces caused by flying through the atmosphere at
      hypersonic speed, as during reentry from space; as,
      ablation of the heat shield during reentry.
      [PJC]

WordNet (r) 3.0 (2006):

ablation
    n 1: surgical removal of a body part or tissue [syn: ablation,
         extirpation, cutting out, excision]
    2: the erosive process that reduces the size of glaciers

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "ablation":
   abrasion, abrasive, absorption, abstraction, assimilation,
   atomization, attrition, breakup, buffing, burning up, burnishing,
   chafe, chafing, consumption, corrosion, crumbling, decay,
   decomposition, decrease, decrement, deduction, degradation,
   deliquescence, depletion, depreciation, detrition, digestion,
   dilapidation, disintegration, disjunction, disorganization,
   dissipation, dissolution, drain, dressing, eating up, erasure,
   erosion, evaporation, exhaustion, expending, expenditure, filing,
   finishing, fretting, galling, grazing, grinding, impoverishment,
   incoherence, ingestion, leakage, limation, loss, polishing,
   purification, rasping, ravages of time, refinement, removal,
   resolution, rubbing away, sandblasting, sanding, scouring, scrape,
   scraping, scratch, scratching, scrub, scrubbing, scuff, shining,
   shrinkage, smoothing, spending, squandering, subduction, sublation,
   subtraction, taking away, use, using, using up, wastage, waste,
   wastefulness, wasting away, wear, wear and tear, wearing,
   wearing away, wearing down, weathering