Egyptian goddess is duplicated (4)
I believe the answer is:
isis
'egyptian goddess' is the definition.
(I've seen this before)
'is duplicated' is the wordplay.
'duplicated' becomes 'is' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is'+'is'='ISIS'
Can you help me to learn more?
(Other definitions for isis that I've seen before include "Oxford's second eight" , "The upper Thames" , "Revered figure" , "Old Egyptian fertility goddess" , "Egyptian deity" .)