Source : Webster's Revised Unabridged Dictionary (1913)

Cannula \Can"nu*la\, n. [L. cannula a small tube of dim. of
   canna a reed, tube.] (Surg.)
   A small tube of metal, wood, or India rubber, used for
   various purposes, esp. for injecting or withdrawing fluids.
   It is usually associated with a trocar. [Written also
   {canula}.]

Source : WordNet®

cannula
     n : a small flexible tube inserted into a body cavity for
         draining off fluid or introducing medication