Note Queen leading state (6)
I believe the answer is:
quaver
'note' is the definition.
(musical note)
'queen leading state' is the wordplay.
'queen' becomes 'qu' (abbreviation for queen).
'leading' means one lot of letters go next to another (some letters go in front of others).
'state' becomes 'aver' (both can mean to declare).
'qu'+'aver'='QUAVER'
(Other definitions for quaver that I've seen before include "Shake; a short note" , "Tremble - half a crotchet" , "(Of voice) tremble" , ".Speak in a trembling voice" , "Tremble; musical note" .)