Toothed fastener (3)
I believe the answer is:
zip
'toothed fastener' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for zip that I've seen before include "drive" , "required in open-and-shut case?" , "Energy (informal); a US code" , "Energy or clothes fastener" , "Sound of bullet passing" .)