Magnate not coy in flotation? (6)
I believe the answer is:
tycoon
'magnate' is the definition.
(I've seen this before)
'not coy in flotation?' is the wordplay.
'in flotation?' indicates anagramming the letters (I've seen 'in flotation' mean this).
'not'+'coy'='notcoy'
'notcoy' is an anagram of 'TYCOON'.
(Other definitions for tycoon that I've seen before include "One very wealthy" , "Big noise" , "Wealthy or powerful business person" , "Rich businessperson" , "Rich and powerful businessman" .)