Noblewoman starts to develop unusual board game (7)
I believe the answer is:
duchess
'noblewoman' is the definition.
(duchess is a kind of noblewoman)
'starts to develop unusual board game' is the wordplay.
'starts to' suggests taking the first letters.
'board game' becomes 'chess' (chess is a kind of board game).
The first letters of 'develop unusual' is 'du'.
'du'+'chess'='DUCHESS'
(Other definitions for duchess that I've seen before include "Great lady" , "Duke's wife" , "Titled lady" , "Titled female" , "Noblewoman" .)