Slayer's genre (5)
I believe the answer is:
metal
'slayer's genre' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for metal that I've seen before include "Substance as gold, iron" , "Eg, titanium" , "Headbanger's music genre" , "Copper possibly" , "Gold or silver in heraldry" .)