'Character' -- a nut wandering about (6)
I believe the answer is:
nature
'character' is the definition.
(thesaurus)
'a nut wandering about' is the wordplay.
'wandering' indicates anagramming the letters.
'about' becomes 're' (regarding**).
'a'+'nut'='anut'
'anut' anagrammed gives 'natu'.
'natu'+'re'='NATURE'
(Other definitions for nature that I've seen before include "Power underlying the world" , "The external, untouched world" , "The physical world" , "Disposition; temper" , "Character (of a person or thing)" .)