Genius? Most are nuts (7)
I believe the answer is:
maestro
'genius?' is the definition.
(thesaurus)
'most are nuts' is the wordplay.
'nuts' indicates anagramming the letters (nuts can mean crazy).
'most'+'are'='mostare'
'mostare' anagrammed gives 'MAESTRO'.
(Other definitions for maestro that I've seen before include "Eminent musician" , "Accomplished musician" , "Some art (anag.)" , "ace" , "Great figure" .)