Illustrious monarch coming in to give power to five at the top (9)
I believe the answer is:
venerable
'illustrious' is the definition.
(thesaurus)
'monarch coming in to give power to five at the top' is the subsidiary indication.
'monarch' becomes 'er' (Abbreviation for Elizabeth Regina).
'coming in to' is an insertion indicator.
'give power to' becomes 'enable' (I've seen this before).
'five' becomes 'v' ('v' can be a synonym of 'five').
'at the top' is a charade indicator (letters next to each other).
'er' inserted into 'enable' is 'enerable'.
'enerable' after 'v' is 'venerable'.
(Other definitions for venerable that I've seen before include "Worthy of reverence" , "like Bede" .)