Dons' home outside University College mess (4)
I believe the answer is:
muck
'mess' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for muck that I've seen before include "Filth, dirt or slime" , "(Spread) manure" , "Filth (where there's brass?)" , "Moist farmyard dung" , "Dirt (associated with brass)" .)