Source : Webster's Revised Unabridged Dictionary (1913)

Fistula \Fis"tu*la\ (?; 135), n.; pl. {Fistul[ae]}. [L.]
   1. A reed; a pipe.

   2. A pipe for convejing water. [Obs.] --Knight.

   3. (Med.) A permanent abnormal opening into the soft parts
      with a constant discharge; a deep, narrow, chronic
      abscess; an abnormal opening between an internal cavity
      and another cavity or the surface; as, a salivary fistula;
      an anal fistula; a recto-vaginal fistula.

   {Incomplete fistula} (Med.), a fistula open at one end only.

Source : WordNet®

fistula
     n 1: a chronic inflammation of the withers of a horse [syn: {fistulous
          withers}]
     2: an abnormal passage leading from a suppurating cavity to the
        body surface [syn: {sinus}]
     [also: {fistulae} (pl)]

fistulae
     See {fistula}