Secure places in favour of locks (10)
I believe the answer is:
fortresses
'secure places' is the definition.
Although both the answer and definition are plural nouns, I don't see how one could define the other.
'in favour of locks' is the wordplay.
'in favour of' becomes 'for' (being for a particular cause).
'locks' becomes 'tresses' (I've seen this before).
'for'+'tresses'='FORTRESSES'
Can you help me to learn more?
(Other definitions for fortresses that I've seen before include "well-defended places" , "citadels" , "defences" .)