Being open, a tin gets sour (7)
I believe the answer is:
candour
'being open' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'a tin gets sour' is the wordplay.
'a tin' becomes 'can' ('can' can be a synonym of 'tin').
'gets' is a charade indicator (letters next to each other).
'sour' becomes 'dour' (synonyms).
'can'+'dour'='CANDOUR'
Can you help me to learn more?
(Other definitions for candour that I've seen before include "Forthrightness" , "Frankness, openness" , "open)" , "telling it like it is" , "Openness, honesty" .)