cath·e·ter (k?th??-t?r)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 kathet?r, from kath?enai, kathe-, to send down : kat-, kata-, cata- + h?enai, to send; see y?- in Indo-European roots.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.catheter (?kæ??t?) n (Medicine) med a long slender flexible tube for inserting into a natural bodily cavity or passage for introducing or withdrawing fluid, such as urine or blood[C17: from Late Latin, from Greek kathet?r, from kathienai to send down, insert]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014cath?e?ter (?kæ? ? t?r) n. a thin flexible tube inserted into a bodily passage, vessel, or cavity to allow fluids to pass into or out of it, to distend it, or to convey diagnostic or other instruments through it. [1595?1605;