### Clue: Mrs Grundy is cautious and wise? Not half! (5)
### Answer: PRUDE 
 ### Explanation: Definition: Mrs Grundy
 "prudential"(cautious and wise/acting carefully and thoughtfully) **minus 5 of its 10 letters**(Not half).
Defn: …/one with very conventional ideas of propriety, originating from the name of a fictional character.