Exploit involving extremely disagreeable undergraduate (7)
I believe the answer is:
student
'undergraduate' is the definition.
(thesaurus)
'exploit involving extremely disagreeable' is the wordplay.
'exploit' becomes 'stunt' (stunt is a kind of exploit**).
'involving' is an insertion indicator.
'extremely' says to hollow out the word (remove centre letters).
'disagreeable' with its centre taken out is 'de'.
'stunt' going around 'de' is 'STUDENT'.
(Other definitions for student that I've seen before include "collegian" , "Scholar" , "One at university" , "Maybe fresher" , "Eg, undergraduate" .)