Bold take-over by the commanding officer on horseback (4)
I believe the answer is:
coup
'bold take-over' is the definition.
I can't judge whether this defines the answer.
'by the commanding officer on horseback' is the wordplay.
'by' says to put letters next to each other.
'the commanding officer' becomes 'co'.
'on horseback' becomes 'up' (up can mean up on a horse).
'co'+'up' is 'COUP'.
Can you help me to learn more?
(Other definitions for coup that I've seen before include "Accomplishment, exploit" , "Clever and succesful strategem" , "Violent seizure of power" , "rising" , "Hostile takeover" .)