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]