A wood on the borders of a local river (7)
I believe the answer is:
spinney
'river' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'a wood on the borders of a local' is the wordplay.
'a wood' becomes 'spiny' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' is an insertion indicator (as in clothing \'on\' a person).
'the borders of' says to hollow out the word (remove centre letters).
'a local' becomes 'native' (I've seen this before).
'native' with its middle taken out is 'ne'.
'spiny' placed around 'ne' is 'SPINNEY'.
Can you help me to learn more?
(Other definitions for spinney that I've seen before include "Small clump of trees" , "little wood" , "Small area of trees" , "Copse of trees" , "Cops, we hear" .)