One right with no returns to a metallic element (4)
I believe the answer is:
iron
'to a metallic element' is the definition.
(iron is a kind of metallic element)
'one right with no returns' is the wordplay.
'one' becomes 'i' (Roman numeral).
'right' becomes 'r' (common abbreviation).
'with' means one lot of letters go next to another.
'returns' is a reversal indicator.
'no' backwards is 'on'.
'i'+'r'+'on'='IRON'
(Other definitions for iron that I've seen before include "Metal (that may be pumped?)" , "used in the evening" , "Metallic chemical element" , "Smooth (clothes)" , "See 14" .)