Unbind (6)
I believe the answer is:
loosen
'unbind' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for loosen that I've seen before include "Make less tight, slacken" , "Undo a little" , "relax or tear apart" , "Untie, relax" , "Relax the tension" .)