Unfasten, remove (6)
I believe the answer is:
detach
I believe this is a double definition.
'unfasten' is the first definition.
(I've seen this in another clue)
'remove' is the second definition.
(I've seen this in another clue)
(Other definitions for detach that I've seen before include "Disengage (something) and remove it" , "The reverse of 11 Down" , "Take away -- the cad (anag)" , "Separate, disconnect" , "His timid love song (T. S. Eliot)" .)