### Clue: Case of chronically having stone in bladder? (4)
### Answer: CYST 
 ### Explanation: Definition: bladder
 **1st and last letters of**(Case of) "chronically" **plus**(having) ST(abbrev. for "stone", the unit of weight).
Defn: In the body, a pocket of tissue containing fluids like a sac/bladder. And cysts may grow (rarely) in one's urinary bladder.