River goddess (4)
I believe the answer is:
isis
I believe this is a double definition.
'river' is the first definition.
(term for the River Thames in Oxford)
'goddess' is the second definition.
(Egyptian god)
(Other definitions for isis that I've seen before include "Egyptian deity" , "academic stream?" , "Si Si - she's an Egyption goddess" , "Old Egyptian fertility goddess" , "Egyptian goddess and jihadist group" .)