Free to unite, possibly (5)
I believe the answer is:
untie
'free' is the definition.
(I've seen this before)
'unite possibly' is the wordplay.
'possibly' is an anagram indicator.
'unite' anagrammed gives 'UNTIE'.
'to' acts as a link.
(Other definitions for untie that I've seen before include "Free from restraining bonds or ropes" , "Undo, unfasten" , "Loose bonds" , "Remove ropes, unfasten" , "Set free" .)