Disposition of aunt changes again (6)
I believe the answer is:
nature
'disposition' is the definition.
(I know that disposition can be written as nature)
'aunt changes again' is the wordplay.
'changes' indicates an anagram.
'again' becomes 're' (prefix meaning 'again').
'aunt' is an anagram of 'natu'.
'natu'+'re'='NATURE'
'of' is the link.
(Other definitions for nature that I've seen before include "Motherly" , "Character, disposition" , "variety" , "scientific journal" , "It abhors a vacuum, according to Aristotle" .)