Loosen, as a lace (5)
I believe the answer is:
untie
'loosen as a lace' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for untie that I've seen before include "get rid of bonds" , "Take off fastenings" , "resolve" , "Set free" , "Free from restraining bonds or ropes" .)