Act before an underling gains control (8)
I believe the answer is:
dominion
'control' is the definition.
(I've seen this before)
'act before an underling' is the wordplay.
'act' becomes 'do' (I've seen this in other clues).
'before' is a charade indicator (letters next to each other).
'an underling' becomes 'minion' (I've seen this before).
'do'+'minion'='DOMINION'
'gains' acts as a link.
(Other definitions for dominion that I've seen before include "Realm" , "Jurisdiction" , "Territorial possession controlled by a ruling state" , "power" , "Sovereignty, control" .)