Bullied little sibling with book bolted (10)
I believe the answer is:
browbeaten
'bullied' is the definition.
('browbeat' can be a synonym of 'bully')
'little sibling with book bolted' is the wordplay.
'little sibling' becomes 'bro' (short for 'brother').
'with' becomes 'w' (short for with).
'book' becomes 'b' (abbreviation for book).
'bolted' becomes 'eaten' (I can't justify this - if you can you should give a lot more credence to this answer).
'bro'+'w'+'b'+'eaten'='BROWBEATEN'
Can you help me to learn more?
(Other definitions for browbeaten that I've seen before include "Bullied" , "Intimidated" .)