Command underling to support party (8)
I believe the answer is:
dominion
'command' is the definition.
(thesaurus)
'underling to support party' is the wordplay.
'underling' becomes 'minion' (I've seen this before).
'to support' says to put letters next to each other (in a down clue, some letters hold others up).
'party' becomes 'do' (do is a kind of party).
'minion' after 'do' is 'DOMINION'.
(Other definitions for dominion that I've seen before include "territory" , "eg Canada" , "Supremacy" , "Sovereignty, control" , "Area of control" .)