I have a little sister at Oxford (4)
I believe the answer is:
isis
'oxford' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'i have a little sister' is the wordplay.
'have' is a charade indicator (letters next to each other).
'a little sister' becomes 'sis' (synonyms. I am not sure about the 'little' bit.).
'i'+'sis'='ISIS'
'at' acts as a link.
Can you help me to learn more?
(Other definitions for isis that I've seen before include "Egypt. goddess" , "Oxford river; goddess" , "Old Egyptian fertility goddess" , "A dark blue flower" , "divinity" .)