Reasons for rejecting upper-class eccentrics (5)
I believe the answer is:
cases
'eccentrics' is the definition.
(I know this)
'reasons for rejecting upper-class' is the wordplay.
'reasons' becomes 'causes' (the reasons for something).
'for rejecting' indicates named letters should be taken away.
'upper-class' becomes 'u' (similar in meaning).
'causes' with 'u' removed is 'CASES'.
(Other definitions for cases that I've seen before include "Lawsuits or travelling containers" , "Pieces of luggage and legal proceedings" , "Bags" , "Proceedings in a court of law" , "Clothes containers or court trials" .)