Source : Webster's Revised Unabridged Dictionary (1913)

Catheter \Cath"e*ter\, n. [L., fr. Gr. ? a thing let down or put
   in, catheter, fr. ? to send down, to let down; ? + ? to
   send.] (Med.)
   The name of various instruments for passing along mucous
   canals, esp. applied to a tubular instrument to be introduced
   into the bladder through the urethra to draw off the urine.

   {Eustachian catheter}. See under {Eustachian}.

   {Prostatic catheter}, one adapted for passing an enlarged
      prostate.

Source : WordNet®

catheter
     n : a thin flexible tube inserted into the body to permit
         introduction or withdrawal of fluids or to keep the
         passageway open