Bareheaded queen on run? Nonsense! (10)
I believe the answer is:
balderdash
'nonsense' is the definition.
(balderdash is a kind of nonsense)
'bareheaded queen on run?' is the wordplay.
'bareheaded' becomes 'bald'.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'on' means one lot of letters go next to another.
'run?' becomes 'dash' (dash is a kind of run**).
'bald'+'er'+'dash'='BALDERDASH'
(Other definitions for balderdash that I've seen before include "Poppycock" , "Nonsense" , "cobblers > GAME" , "Bunk" , "garbage" .)