Half of root vegetable left to go bad (3)
I believe the answer is:
rot
'go bad' is the definition.
(I've seen this in another clue)
'half of root vegetable' is the wordplay.
'half of' suggests halving the letters.
'root vegetable' becomes 'carrot' (carrot is a kind of root vegetable).
'carrot' cut in half is 'ROT'.
'left to' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for rot that I've seen before include "'Decay, decompose (3)'" , "Paradise" , "Gradual decline" , "Corruption" , "Decay, wither" .)