Fellow entertained by Londoners (3)
I believe the answer is:
don
'fellow' is the definition.
(both can mean an academic)
'entertained by londoners' is the wordplay.
'entertained by' indicates the answer is hidden within the clue (the clue hosts or entertains the answer).
'DON' is hidden within 'londoners'.
(Other definitions for don that I've seen before include "put on > one of several rivers" , "Mafia supremo" , "Put on the learned man" , "Bradman, the ---" , "Flower" .)