Business leader (4)
(Other definitions for boss that I've seen before include "Person in charge - raised knob" , "Stud; employer" , "designer" , "Stud; chief" , "One managing" .)
'business leader' is the definition.
(synonyms)
This is all the clue.
(Other definitions for magnate that I've seen before include "Fellow with a lot of money" , "Fat cat" , "Important fellow" , "Wealthy business leader" , "Tycoon" .)