Contrary pharaoh censures them, discovering it's an imitation (4)
I believe the answer is:
echo
'it's an imitation' is the definition.
(I know that echo is a type of imitation)
'contrary pharaoh censures them discovering' is the wordplay.
'contrary' is a reversal indicator.
'discovering' indicates the answer is hidden within the clue (I've seen 'discovered' mean this (remove the letters covering the answer in the clue)).
'ohce' is hidden within 'pharaoh censures them'.
'ohce' in reverse letter order is 'ECHO'.
(Other definitions for echo that I've seen before include "Bounced sound" , "repetitive" , "Reminder" , "Nymph whose love Narcissus spurned" , "A natural sound reflection" .)