Coup deposes king for progress (9)
I believe the answer is:
evolution
'progress' is the definition.
(thesaurus)
'coup deposes king' is the wordplay.
'coup' becomes 'revolution' (change of government).
'deposes' is a deletion indicator.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'revolution' with 'r' taken out is 'EVOLUTION'.
'for' is the link.
(Other definitions for evolution that I've seen before include "Darwin's theory" , "Slow change" , "Darwinian process" , "Gradual change" , "it's a gradual process" .)