Heading off for relative release (5)
I believe the answer is:
untie
'release' is the definition.
(eg to untie restraints)
'heading off for relative' is the wordplay.
'heading off for' means to remove the first letter.
'relative' becomes 'auntie' (auntie is a kind of relative).
'auntie' with its initial letter removed is 'UNTIE'.
(Other definitions for untie that I've seen before include "Loose bonds" , "Loosen, as laces" , "Open a knot" , "Release (knots)" , "Detach" .)