Iron originally included in standard brace (4)
I believe the answer is:
pair
'brace' is the definition.
(synonyms)
'iron originally included in standard' is the wordplay.
'originally' indicates taking the first letters.
'included in' indicates putting letters inside.
'standard' becomes 'par' (I've seen this before).
The initial letter of 'iron' is 'i'.
'i' going into 'par' is 'PAIR'.
(Other definitions for pair that I've seen before include "Duo" , "2" , "Two of a kind, as in cards" , "how braces come" , "Set of two" .)