Royal about in military display (7)
I believe the answer is:
monarch
'royal' is the definition.
(thesaurus)
'about in military display' is the wordplay.
'about' becomes 'on' (as in a book 'on' a certain topic).
'in' is an insertion indicator.
'military display' becomes 'march' (I can't justify this - if you can you should believe this answer much more).
'on' put into 'march' is 'MONARCH'.
Can you help me to learn more?
(Other definitions for monarch that I've seen before include "Eg, king, queen, emperor" , "Butterfly - ruler" , "Sovereign; butterfly" , "Not a subject" , "Crowned head" .)