- Any enveloping structure, such as the membranous covering of a muscle, nerve, or blood vessel. Any sheathlike structure.
- The prepuce of male animals, especially of the horse.
- A specially designed tubular instrument through which special obturators or cutting instruments can be passed, or through which blood clots, tissue fragments, and calculi can be evacuated.
- A tube used as an orthodontic appliance, usually on molars.