Get iron modified with new element (8)
I believe the answer is:
nitrogen
'element' is the definition.
(chemical element)
'get iron modified with new' is the wordplay.
'modified with' indicates anagramming the letters.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'get'+'iron'='getiron'
'getiron' mixed up with 'n' gives 'NITROGEN'.
(Other definitions for nitrogen that I've seen before include "Chemical element" , "It constitutes 78 percent of the atmosphere" , "Constituent of four fifths of earth's atmosphere" , "It makes up 78% of air" , "creates much atmosphere" .)