In hindsight, somewhat regret a contract's provision (5)
I believe the answer is:
cater
'provision' is the definition.
(I've seen this before)
'in hindsight somewhat regret a contract's' is the wordplay.
'in hindsight' says the letters should be written in reverse (hindsight is looking back).
'somewhat' indicates the answer is hidden within the clue.
'retac' is hidden in the letters of 'regret a contracts'.
'retac' reversed gives 'CATER'.
(Other definitions for cater that I've seen before include "Provide food and drink (for an event)" , "Supply provisions" , "Trace (anag.)" , "Provide services, food or entertainment" , "Supply food for parties" .)