The cow's outside (7)
I believe the answer is:
leather
'the cow's outside' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'the cow's outside' is the wordplay.
'cow's' becomes 'lear' (I can't justify this - if you can you should give a lot more credence to this answer).
'outside' is an insertion indicator (some letters go outside others).
'the' going into 'lear' is 'LEATHER'.
Can you help me to learn more?
(Other definitions for leather that I've seen before include "Treated hide" , "Whip" , "Polishing cloth" , "A tanner produces it from hide" , "Tanned animal hide" .)