Relative to a release (6)
I believe the answer is:
auntie
'relative' is the definition.
(auntie is a kind of relative)
'a release' is the wordplay.
'release' becomes 'untie' (eg to untie restraints).
'a'+'untie'='AUNTIE'
'to' is the link.
(Other definitions for auntie that I've seen before include "Female relative" , "Unite a strange family member" , "The Beeb" , "Relation; the BBC" , "woman in the family" .)