Copious work mostly contributed (7)
I believe the answer is:
opulent
'copious' is the definition.
(thesaurus)
'work mostly contributed' is the wordplay.
'work' becomes 'opus' (an opus is an artistic work).
'mostly' means to remove the last letter (most but not all of the word).
'contributed' becomes 'lent' ('lend' can be a synonym of 'contribute').
'opus' with its last letter taken off is 'opu'.
'opu'+'lent'='OPULENT'
(Other definitions for opulent that I've seen before include "Wealthy, possessing riches" , "'Rich, luxurious (7)'" , "'Loaded'" , "Luxurious or profuse" , "Moneyed" .)