Queen isn't commonly charming! (6)
I believe the answer is:
quaint
'charming' is the definition.
(I've seen this before)
'queen isn't commonly' is the wordplay.
'queen' becomes 'qu'.
'isn't commonly' becomes 'aint' (I've seen this in other clues).
'qu'+'aint'='QUAINT'
(Other definitions for quaint that I've seen before include "Attractively odd" , "Charming" , "Charmingly odd, old" , "Picturesque" , "Attractive, in an old-fashioned way" .)