Bound to admit sin if panic-stricken (9)
I believe the answer is:
terrified
'panic-stricken' is the definition.
('terrified' can be a synonym of 'panic-stricken')
'bound to admit sin if' is the wordplay.
'bound' becomes 'tied' (I've seen this before**).
'to admit' is an insertion indicator.
'sin' becomes 'err' (to sin is to err morally).
'err'+'if'='errif'
'tied' placed around 'errif' is 'TERRIFIED'.
(Other definitions for terrified that I've seen before include "Panic-stricken - dire refit (anag)" , "Scared stiff" , "Greatly frightened" , "Extremely frightened" .)