Top of bill, moi! (4)
I believe the answer is:
acme
'top' is the definition.
('acme' can be a synonym of 'top')
'bill moi' is the wordplay.
'bill' becomes 'ac'.
'moi' becomes 'me' (French, and used for comic effect in English).
'ac'+'me'='ACME'
'of' is the link.
(Other definitions for acme that I've seen before include "Summit - climax" , "Top or highest point" , "Summit - zenith" , "Zenith - optimum" , "Pinnacle" .)