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.
- Pathology An abnormal membranous sac containing a gaseous, liquid, or semisolid substance.
- Anatomy A sac or vesicle in the body.
- Biology A small capsulelike sac that encloses certain organisms in their dormant or larval stage.
- Botany A thick-walled resting spore, as in certain algae or fungi.