Cyst

1. n. A form assumed by Protozoa in which they become saclike and quiescent. It generally precedes the production of germs. See Encystment.
2. n. 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.
3. n. In old authors, the urinary bladder, or the gall bladder.
4. n. One of the bladders or air vessels of certain algae, as of the great kelp of the Pacific, and common rockweeds (Fuci) of our shores.
5. n. 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.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.