Garment fastener comes with a warning (8)
I believe the answer is:
pinafore
'garment' is the definition.
(pinafore is a kind of garment)
'fastener comes with a warning' is the wordplay.
'fastener' becomes 'pin' (pin is a kind of fastener).
'comes with' means one lot of letters go next to another.
'warning' becomes 'fore' (shouted in golf).
'pin'+'a'+'fore'='PINAFORE'
(Other definitions for pinafore that I've seen before include "Protective gear" , "'HMS - - ' G & S" , "HMS -- (G&S)" , "Stagecraft, say" , "Protective garment worn over front" .)