A person's character aunt is upset about (6)
I believe the answer is:
nature
'a person's character' is the definition.
'nature' can be an answer for 'character' (thesaurus). I'm unsure of the 'a person's' bit.
'aunt is upset about' is the wordplay.
'is upset' indicates anagramming the letters.
'about' becomes 're' (regarding).
'aunt' anagrammed gives 'natu'.
'natu'+'re'='NATURE'
Can you help me to learn more?
(Other definitions for nature that I've seen before include "Disposition, temperament" , "mother, so-called" , "It abhors a vacuum, according to Aristotle" , "type?" , "Mother Earth" .)