New union member to live free within (5)
I believe the answer is:
bride
'new union member' is the definition.
(I've seen this before)
'live free within' is the wordplay.
'live' becomes 'be' (synonyms).
'free' becomes 'rid' (synonyms).
'within' is an insertion indicator.
'be' enclosing 'rid' is 'BRIDE'.
'to' acts as a link.
(Other definitions for bride that I've seen before include "Female at match" , "She's just about to be married" , "presumably honeymoon for me?" , "Newlywed" , "woman in front of train" .)