-cyst n combining form (Biology) indicating a bladder or sac: otocyst. [from Greek kustis bladder]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014cyst (s?st) n. 1. any abnormal saclike growth of the body in which matter is retained. 2. a bladder, sac, or vesicle. 3. a. a protective capsule or spore surrounding an inactive or resting organism or a reproductive body. b. such a capsule and its contents. [1705?15;