Group has a chair (4)
I believe the answer is:
seat
'chair' is the definition.
(thesaurus)
'group has a' is the wordplay.
'group' becomes 'set' (set is a kind of group**).
'has' means one lot of letters goes inside another.
'set' enclosing 'a' is 'SEAT'.
(Other definitions for seat that I've seen before include "Box ---, position of advantage" , "MP's constituency" , "Parliamentary constituency" , "pew?" , "Chair, bench, saddle, etc" .)