Oxbridge professor is a gentleman from Spain (3)
I believe the answer is:
don
This clue could be a double definition.
'oxbridge professor' is the first definition.
'don' can be an answer for 'professor' (term for a university professor). I'm not certain of the 'oxbridge' bit.
'gentleman from spain' is the second definition.
(formal term of address for a man in Spanish)
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for don that I've seen before include "Put on; lecturer" , "Get into" , "Mafia chief or Spanish title" , "University teacher" , "A Spanish grandee like Quixote" .)