Castle geared toward getting lock (8)
I believe the answer is:
fortress
'castle' is the definition.
(I've seen this before)
'getting lock' is the wordplay.
'getting' becomes 'for' (I can't explain this - if you can you should give a lot more credence to this answer).
'lock' becomes 'tress' (I've seen this before).
'for'+'tress'='FORTRESS'
'geared toward' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for fortress that I've seen before include "Fortified defensive structure" , "it's hard to break into" , "Strong point" , "Protective structure" , "Military stronghold" .)