Interjection that's archaic, say, in the current era (4)
I believe the answer is:
egad
'interjection that's archaic' is the definition.
'say in the current era' is the wordplay.
'say' becomes 'eg'.
'in the current era' becomes 'ad'.
'eg'+'ad'='EGAD'
(Other definitions for egad that I've seen before include "Old exclamation; aged (anagram)" , "Forgotten curse" , "Mild oath - aged (anag)" , "Christ" , "Oath sworn" .)