Fruit is good to use again (9)
I believe the answer is:
greengage
'fruit' is the definition.
(type of plum)
'good to use again' is the wordplay.
I cannot really understand how this works, but
'good' could be 'g' (abbreviation) and 'g' is present in the answer.
'again' could be 're' (prefix meaning 'again') and 're' is located in the answer.
The remaining letters 'engage' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for greengage that I've seen before include "Fruit tree" , "Fruit like a small plum" , "Garden fruit" , "Greenish-yellow type of plum" , "Fruit akin to plum" .)