n 1  :  a closed sac having a distinct membrane and developing abnormally in a body cavity or structure  2  :  a body resembling a cyst: as  a  :  a capsule formed about a minute organism going into a resting or spore stage : also  :  this capsule with its contents  b  :  a resistant cover about a parasite produced by the parasite or the host - compare HYDATID2a   .
 
 
 
Published under license with Merriam-Webster, Incorporated.  © 1997-2024.