Ours is sour (7)
I believe the answer is:
anagram
'sour' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for anagram that I've seen before include "Word rearranging another's letters" , "Word(s) rearranged to form others" , "A ragman (anag)" , "Hedonism for Sondheim" , "Nag a ram (anag)" .)