Rich fellow’s finally given a shilling (5)
I believe the answer is:
nabob
'rich fellow's' is the definition.
'finally given a shilling' is the wordplay.
'finally' suggests the final letters.
'shilling' becomes 'bob'.
The last letter of 'given' is 'n'.
'n'+'a'+'bob'='NABOB'
(Other definitions for nabob that I've seen before include "Wealthy influential person" , "Person of great wealth" , "Person of conspicuous wealth or high status" , "VIP" , "Mogul governor; very rich or important person" .)