Lock for abandoned castle (5)
I believe the answer is:
tress
This could be a double definition.
'lock' is the first definition.
(both can mean a piece of hair)
'abandoned castle' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'for' is the link.
Can you help me to learn more?
(Other definitions for tress that I've seen before include "Switch" , "Long piece of hair" , "Rests (anag.)" , "Curl - lock" , "is a bit of a shock" .)