a closed sac, e.g. of watery liquid or gas, with a distinct membrane, esp one developing abnormally in a plant or animal
a micro-organism in a resting or spore stage, or a capsule formed about it
a resistant cover formed about a parasite when inside the host
cystoid /ʹsistoyd/ adj and noun
[scientific Latin cystis from Greek kystis bladder, pouch]