Metal split into many (8)
I believe the answer is:
antimony
'metal' is the definition.
(antimony is a kind of metal)
'split into many' is the wordplay.
'split' indicates anagramming the letters (letters split up and reassembled).
'into'+'many'='intomany'
'intomany' anagrammed gives 'ANTIMONY'.
(Other definitions for antimony that I've seen before include "Toxic metallic element used in semiconductors" , "Bluish-white element, symbol Sb" , "One element" , "My nation (anag) - metallic element" , "Brittle element" .)