Quixotic former queen going to rave (6)
I believe the answer is:
errant
'quixotic' is the definition.
(I've seen this before)
'former queen going to rave' is the wordplay.
'former queen' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'going to' is a charade indicator (letters next to each other).
'rave' becomes 'rant' (synonyms).
'er'+'rant'='ERRANT'
(Other definitions for errant that I've seen before include "heretical?" , "Misbehaving" , "Quixotic" , "Travelling about or going astray" , "Off the mark, wandering" .)