Command a slave to serve one first (8)
I believe the answer is:
dominion
'command' is the definition.
(thesaurus)
'a slave to serve one first' is the wordplay.
'a slave' becomes 'minion' (I can't justify this - if you can you should give a lot more credence to this answer).
'to serve' becomes 'do' (synonyms).
'one first' says to put letters next to each other.
'minion' after 'do' is 'DOMINION'.
Can you help me to learn more?
(Other definitions for dominion that I've seen before include "Authority to rule over and control people" , "Realm" , "Supremacy" , "Sovereignty, control" , "Area of control" .)