Nancy's to dine, hosting a boss (7)
I believe the answer is:
manager
'boss' is the definition.
(thesaurus)
'nancy's to dine hosting a' is the wordplay.
'nancy's to dine' becomes 'manger' ('to eat' in French - Nancy is a French city).
'hosting' is an insertion indicator.
'manger' placed around 'a' is 'MANAGER'.
(Other definitions for manager that I've seen before include "executive position" , "Sports team controller" , "Organiser" , "Person in charge of staff" , "Boss" .)