The Collaborative International Dictionary of English v.0.48:

Incision \In*ci"sion\, n. [L. incisio: cf. F. incision. See
   Incise.]
   [1913 Webster]
   1. The act of incising, or cutting into a substance;
      specifically: (Med.) the cutting action made during
      surgery to gain access to the body parts under the skin.
      --Milton.
      [1913 Webster +PJC]

   2. That which is produced by incising; the separation of the
      parts of any substance made by a cutting or pointed
      instrument; a cut; a gash; specifically (Med.) the cut in
      the skin made during surgery to gain access to the
      interior of the body.
      [1913 Webster +PJC]

   3. Separation or solution of viscid matter by medicines.
      [Obs.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

incision
    n 1: a depression scratched or carved into a surface [syn:
         incision, scratch, prick, slit, dent]
    2: the cutting of or into body tissues or organs (especially by
       a surgeon as part of an operation) [syn: incision,
       section, surgical incision]

Moby Thesaurus II by Grady Ward, 1.0:

167 Moby Thesaurus words for "incision":
   abrasion, abysm, abyss, arroyo, bezel, blaze, blemish, box canyon,
   breach, break, burn, burr, canyon, cavity, chafe, chamfer, chap,
   chase, chasm, check, chimney, chink, chip, chiseling, cleft,
   cleuch, clough, col, concussion, corrugation, coulee, couloir,
   crack, crackle, cranny, craze, crena, crevasse, crevice,
   cross-hatching, cut, cwm, dado, defile, dell, demitint, depression,
   dike, ditch, donga, draw, engravement, engraving, etch, etching,
   excavation, fault, fissure, flash burn, flaw, flume, flute,
   fluting, fracture, fray, frazzle, furrow, gall, gap, gape, gash,
   gem-engraving, glass-cutting, glyptic, gorge, gouge, graving,
   groove, gulch, gulf, gully, hack, half tint, hatching, hole, hurt,
   indentation, injury, inscript, inscription, jag, jog, joggle,
   joint, kerf, kloof, laceration, leak, lesion, line, lining,
   marking, microgroove, moat, mortal wound, mutilation, nick, nock,
   notch, nullah, opening, pass, passage, puncture, rabbet, ravine,
   rent, rifling, rift, rime, rip, ruck, run, rupture, rut, scald,
   scissure, scorch, score, scoring, scotch, scrape, scratch,
   scratching, scuff, seam, second-degree burn, slash, slashing, slit,
   slot, sore, split, stab, stab wound, stipple, stippling, streak,
   stria, striation, sulcation, sulcus, tear, third-degree burn, tint,
   tooling, trauma, trench, type-cutting, valley, void, wadi,
   well-worn groove, wound, wounds immedicable, wrench, wrinkle