Frightening year out for Mark (4)
I believe the answer is:
scar
'mark' is the definition.
('scar' can be a synonym of 'mark')
'frightening year out' is the wordplay.
'frightening' becomes 'scary' (I've seen this before).
'year' becomes 'y'.
'out' is a deletion indicator.
'scary' with 'y' taken out is 'SCAR'.
'for' is the link.
(Other definitions for scar that I've seen before include "Sign of wound" , "Injury mark - cliff" , "Old wound - bare cliff" , "One left after having wound" , "Effect of unpleasant experience" .)