Key locks office (5)
I believe the answer is:
chair
'office' is the definition.
(both can mean a position of authority)
'key locks' is the wordplay.
'key' becomes 'c' (musical key).
'locks' becomes 'hair' (I've seen this before).
'c'+'hair'='CHAIR'
(Other definitions for chair that I've seen before include "Backed seat for one" , "Academic position" , "conduct" , "Prof's post; meeting leader" , "president" .)