Pharaohs in Aida retaining Biblical mount (5)
I believe the answer is:
sinai
'biblical mount' is the definition.
(I've seen this before)
'pharaohs in aida retaining' is the wordplay.
'retaining' indicates the answer is hidden within the clue.
'SINAI' is hidden within 'pharaohs in aida'.
(Other definitions for sinai that I've seen before include "Deserted area" , "Biblical mount" , "Peninsula, mostly desert, at north end of Red Sea" , "Mount on which Moses received the Ten Commandments" , "11 Across peninsula" .)