Still in HQ, cautious to oust leader (10)
I believe the answer is:
stationary
'still' is the definition.
(both can mean immobile)
'hq cautious to oust leader' is the wordplay.
'hq' becomes 'station' (I can't explain this - if you can you should give a lot more credence to this answer).
'cautious' becomes 'wary' (similar in meaning).
'to oust leader' means to remove the first letter.
'wary' with its first letter removed is 'ary'.
'station'+'ary'='STATIONARY'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for stationary that I've seen before include "Static" , "Fixed" , "Unmoving" , "Motionless" , "Parking" .)