Treat ’em as identical (4)
I believe the answer is:
same
'identical' is the definition.
('same' can be similar in meaning to 'identical')
'treat 'em as' is the wordplay.
'treat' indicates an anagram.
'em'+'as'='emas'
'emas' is an anagram of 'SAME'.
(Other definitions for same that I've seen before include "If - be the food of love, play on (Twelfth Night)" , "Identical, unchanged" , "Identical, not different" , "Equal in amount or value" , "Aforesaid" .)