The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

   Eustachian catheter. See under Eustachian.

   Prostatic catheter, one adapted for passing an enlarged
      prostate.
      [1913 Webster] Catheterism

WordNet (r) 3.0 (2006):

catheter
    n 1: a thin flexible tube inserted into the body to permit
         introduction or withdrawal of fluids or to keep the
         passageway open