Loosen, open (8)
I believe the answer is:
unfasten
This clue is a double definition.
'loosen' is the first definition.
(I've seen this before)
'open' is the second definition.
(unfastening is a kind of opening)
(Other definitions for unfasten that I've seen before include "Nun's fate (anag.)" , "Unlock" , "Let go" , "Loosen or open, say seatbelt" , "Undo" .)