Side-pain saves nine if in time (6)
I believe the answer is:
stitch
'in time' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'side-pain saves nine' is the wordplay.
'side' means to remove the middle letters (I've seen 'sides of' mean this (only the letters on the sides remain)).
'pain' becomes 'smart' (smart is a kind of pain).
'saves nine' becomes 'itch' (I can't explain this - if you can you should believe this answer much more).
'smart' with its centre removed is 'st'.
'st'+'itch'='STITCH'
'if' acts as a link.
Can you help me to learn more?
(Other definitions for stitch that I've seen before include "One in time is said to save nine" , "Application of needle produces this" , "Having very little to wear" , "Pain in the side brought on by exercise" , "Sharp pain in side of body caused by exercise" .)