Rambling harangue in support of Her Majesty (6)
I believe the answer is:
errant
'rambling' is the definition.
(I've seen this before)
'harangue in support of her majesty' is the wordplay.
'harangue' becomes 'rant' (synonyms).
'in support of' says to put letters next to each other (I've seen this in other clues).
'her majesty' becomes 'ER' (Elizabeth Regina).
'rant' put after 'er' is 'ERRANT'.
(Other definitions for errant that I've seen before include "Straying; knight" , "Rambling" , "Nomadic" , "looking for adventure" , "Wayward - ranter (anag)" .)