Catheter (noun)

1. A thin, flexible tube inserted into the body to allow the passage of fluids or to keep a passage open.
2. A tube that is inserted into a body cavity, duct, or vessel to allow the passage of fluids or to keep the passage open.

Origin:

Late middle english (in the sense "catholic"): from old french catheter, from greek kathetēr "sending down, instrument for letting down", from kathetos "let down", from kata "down" + hienai "to send".

Examples:

1. The patient had a catheter inserted to drain urine from the bladder.
2. A catheter was inserted to measure the pressure in the patient's heart.
3. The catheter was used to administer medication directly into the bloodstream.
4. The catheter was used to measure the pressure inside the patient's lungs.
5. The catheter was used to remove fluid from the patient's lungs.