Control party lackey (8)
I believe the answer is:
dominion
'control' is the definition.
(I know that dominion is a type of control)
'party lackey' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'lackey' becomes 'minion' (both can mean an assistant or henchperson).
'do'+'minion'='DOMINION'
(Other definitions for dominion that I've seen before include "Sovereignty, control" , "Jurisdiction" , "Realm" , "eg Canada" , "power" .)