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

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "catheter":
   adjutage, drainpipe, efflux tube, fire hose, flue pipe, funnel,
   garden hose, gas pipe, hose, hosepipe, nipple, organ pipe, pipe,
   pipeline, pipette, piping, reed, reed pipe, siamese,
   siamese connection, siphon, snorkel, soil pipe, standpipe,
   steam pipe, stem, straw, tap, tube, tubing, tubulation, tubule,
   tubulet, tubulure, waste pipe, water pipe