Pharaoh's river (4)
I believe the answer is:
nile
'pharaoh's river' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nile that I've seen before include "Take a line to the river" , "River associated with Cleopatra" , "Current" , "River (which is originally blue and white)" , "Long river" .)