| n. | 1. | (Med.) A pouch or sac without opening, usually membranous and containing morbid matter, which is accidentally developed in one of the natural cavities or in the substance of an organ. |
| 2. | (Bot.) One of the bladders or air vessels of certain algæ, as of the great kelp of the Pacific, and common rockweeds (Fuci) of our shores. | |
| 3. | (Zool.) A small capsule or sac of the kind in which many immature entozoans exist in the tissues of living animals; also, a similar form in Rotifera, etc. |
| Noun | 1. | cyst - a closed sac that develops abnormally in some body structure |
| 2. | cyst - a small anatomically normal sac or bladderlike structure (especially one containing fluid) Synonyms: vesicle |