Controlling chap meeting duke in Advent? (10)
I believe the answer is:
commanding
'controlling' is the definition.
('command' can be a synonym of 'control')
'chap meeting duke in advent?' is the wordplay.
'chap meeting' becomes 'man' (I can't explain this - if you can you should believe this answer much more).
'duke' becomes 'd'.
'in' means one lot of letters goes inside another.
'advent?' becomes 'coming' ('coming' can be a synonym of 'advent').
'man'+'d'='mand'
'mand' put into 'coming' is 'COMMANDING'.
(Other definitions for commanding that I've seen before include "Powerful" , "Impressive" .)