Second Mrs Grundy’s young man? (5)
I believe the answer is:
sprig
'young man?' is the definition.
(I've seen this before)
'second mrs grundy's' is the wordplay.
I cannot really understand how this works, but
'second' could be 's' (common abbreviation) and 's' is located in the answer.
The remaining letters 'prig' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sprig that I've seen before include "Headless nail; leafy ornament" , "Young family member; small stem" , "Young man" , "Grips with a small branch" , "Purloined" .)