Cyst

Cyst Cyst (s[i^]st), n. [Gr. ky`stis bladder, bag, pouch, fr. ky`ein to be pregnant. Cf. {Cyme}.] 1. (Med.) (a) 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. (b) In old authors, the urinary bladder, or the gall bladder. [Written also {cystis}.] [1913 Webster]

2. (Bot.) One of the bladders or air vessels of certain alg[ae], as of the great kelp of the Pacific, and common rockweeds ({Fuci}) of our shores. --D. C. Eaton. [1913 Webster]

3. (Zo["o]l.) (a) 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. (b) A form assumed by Protozoa in which they become saclike and quiescent. It generally precedes the production of germs. See {Encystment}. [1913 Webster]