Get iron transmuted with new element (8)
I believe the answer is:
nitrogen
'element' is the definition.
(chemical element)
'get iron transmuted with new' is the wordplay.
'transmuted with' indicates anagramming the letters.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'get'+'iron'='getiron'
'getiron' mixed up with 'n' can make 'NITROGEN'.
(Other definitions for nitrogen that I've seen before include "It comprises about four-fifths of the atmosphere" , "It makes up 78% of air" , "Gaseous element" , "Atomic number 7" , "It forms the greater part of air" .)