A queen, gracious host (4)
I believe the answer is:
army
'host' is the definition.
(thesaurus)
'a queen gracious' is the wordplay.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'gracious' becomes 'my' (I've seen this in other clues).
'a'+'r'+'my'='ARMY'
(Other definitions for army that I've seen before include "fighters" , "Fighting force" , "Large military body" , "A defence force" , "Ground forces" .)