Remove, as a seatbelt (8)
I believe the answer is:
unfasten
'remove as a seatbelt' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for unfasten that I've seen before include "Loosen or open, say seatbelt" , "Let go" , "tie? No" , "Unlock" , "Undo" .)