Mistake if kept in bound and frightened (9)
I believe the answer is:
terrified
'frightened' is the definition.
(terrifying is a kind of frightening)
'mistake if kept in bound' is the wordplay.
'mistake' becomes 'err' (synonyms).
'kept in' is an insertion indicator.
'bound' becomes 'tied' (similar in meaning).
'err'+'if'='errif'
'errif' going into 'tied' is 'TERRIFIED'.
'and' is the link.
(Other definitions for terrified that I've seen before include "Extremely frightened" , "Scared stiff" , "Panic-stricken - dire refit (anag)" , "Greatly frightened" .)