What one may do after a fault in supply (7)
I believe the answer is:
reserve
'supply' is the definition.
(thesaurus)
'what one may do after a fault' is the wordplay.
I cannot quite understand how this works, but
'do' could be 'serve' (synonyms) and 'serve' is found in the answer.
The remaining letters 're' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for reserve that I've seen before include "Bank" , "keep for oneself" , "Hold back" , "Order" , "8 [RESTRAINT]" .)