Ours turned resentful (4)
I believe the answer is:
sour
'resentful' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'ours turned' is the wordplay.
'turned' indicates anagramming the letters.
'ours' with letters rearranged gives 'SOUR'.
Can you help me to learn more?
(Other definitions for sour that I've seen before include "Tasting like 1 Dn" , "Acrid or sullen" , "Tart, acidic" , "Sharp- or tart-tasting" , "Having an acidic taste" .)