cyst cyst /ˈsɪst/

noun

1. () A closed sac that develops abnormally in some body structure  ( cyst )
   a closed sac that develops abnormally in some body structure
     The surgeon removed the cyst from the patient's ovary.
   The surgeon removed the cyst from the patient's ovary.
   
   
2. A small anatomically normal sac or bladderlike structure (especially one containing fluid)  ( cyst , vesicle )
   a small anatomically normal sac or bladderlike structure (especially one containing fluid)