Wealthy upper-class fast to support surgeon's work (7)
I believe the answer is:
opulent
'wealthy' is the definition.
(opulent means extravagantly wealthy)
'upper-class fast to support surgeon's work' is the wordplay.
'upper-class' becomes 'u' (similar in meaning).
'fast' becomes 'lent' (Lent is a period of fasting in Christianity).
'to support' says to put letters next to each other (in a down clue, some letters hold others up).
'surgeon's work' becomes 'op' (op can mean a surgery or operation).
'u'+'lent'='ulent'
'ulent' put after 'op' is 'OPULENT'.
(Other definitions for opulent that I've seen before include "Well-to-dp. affluent" , "extremely elegant" , "Let up on, being wealthy" , "'Loaded'" , "Well-to-do or lavish" .)