Sullen medic outside Oxford University (4)
I believe the answer is:
dour
'sullen' is the definition.
(I've seen this before)
'medic outside oxford university' is the wordplay.
'medic' becomes 'dr' (**).
'outside oxford' indicates putting letters inside (I've seen this in other clues).
'university' becomes 'ou'.
'dr' placed around 'ou' is 'DOUR'.
(Other definitions for dour that I've seen before include "Dreary" , "'Sullen, sour (4)'" , "Sullen, severe" , "Severe, stern, gloomy" , "Gloomy-looking, stern" .)