Seat of 100 locks? (5)
I believe the answer is:
chair
'seat' is the definition.
(I know that seat can be written as chair)
'100 locks?' is the wordplay.
'h00' becomes 'c' (Roman numeral).
'locks?' becomes 'hair' (locks can mean hair).
'c'+'hair'='CHAIR'
'of' is the link.
(Other definitions for chair that I've seen before include "Item of furniture (which can be addressed!)" , "Most important seat in committee" , "Official position of authority" , "director at meeting" , "Top seat of committee" .)