Nothing to fasten garment (3)
I believe the answer is:
zip
I believe this clue is a double definition.
'nothing' is the first definition.
(I know that nothing can be written as zip)
'to fasten garment' is the second definition.
(do up a zip)
(Other definitions for zip that I've seen before include "Energy (informal); a US code" , "Locking device with two toothed edges and a sliding tab" , "Nothing < close up" , "tear" , "Type of fastener" .)