Fuse, as metal (4)
I believe the answer is:
weld
'fuse as metal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for weld that I've seen before include "Join by fusion; dye plant" , "Solder" , "Type of metal joint" , "Lewd (anag.)" , "Join; fuse" .)