Rich upstart involved in work, advanced (7)
I believe the answer is:
opulent
'rich' is the definition.
(similar in meaning)
'upstart involved in work advanced' is the wordplay.
'upstart' becomes 'u' (start of the word 'up').
'involved in' is an insertion indicator.
'work' becomes 'op' (common abbreviation for 'opus').
'advanced' becomes 'lent' (advance can mean to lend).
'op'+'lent'='oplent'
'u' inserted into 'oplent' is 'OPULENT'.
(Other definitions for opulent that I've seen before include "Wealthy, rich" , "'Deluxe, luxurious (7)'" , "Well-to-do, rich" , "Moneyed" , "Rolling" .)