cath·e·ter 
(kăthĭ-tər)
(kăthĭ-tər)n.
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.
[Late Latin, from Greek kathetēr, from kathīenai, kathe-, to send down : kat-, kata-, cata- + hīenai, to send; see yē- in the Appendix of Indo-European roots.]