a slender, hollow tube, as of metal or rubber, inserted into a body passage, vessel, or cavity for passing fluids, making examinations, etc., esp. one for draining urine from the bladder
See catheter in American Heritage Dictionary 4
(kăthˈĭ-tər)
noun
A hollow flexible tube for insertion into a body cavity, duct, or vessel to allow the passage of fluids or distend a passageway. Its uses include the drainage of urine from the bladder through the urethra or insertion through a blood vessel into the heart for diagnostic purposes.