Equal with one brace (4)
I believe the answer is:
pair
'brace' is the definition.
(a brace is a pair of something)
'equal with one' is the wordplay.
'equal' becomes 'par'.
'with' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'par' placed around 'i' is 'PAIR'.
(Other definitions for pair that I've seen before include "Cereal used as food" , "how braces come" , "2" , "flight of stairs" , "Husband and wife" .)