It's bound to be Edward that's out of line (4)
I believe the answer is:
tied
'it's bound' is the definition.
('tie' can be a synonym of 'bind')
'edward that's out of line' is the wordplay.
'edward' becomes 'ted'.
'that's' becomes 'ie' (abbreviation for 'id est', 'that is' in Latin).
'out of' means to remove the last letter (I've seen 'out' mean this).
'line' indicates putting letters inside.
'ie' with its final letter taken off is 'i'.
'ted' going around 'i' is 'TIED'.
'to be' is the link.
(Other definitions for tied that I've seen before include "Restricted, bound" , "have equal scores" , "Fastened, bound" , "Knotted" , "Fastened with string" .)