Sodium affected true character (6)
I believe the answer is:
nature
'character' is the definition.
(I've seen this before)
'sodium affected true' is the wordplay.
'sodium' becomes 'NA' (chemical symbol).
'affected' indicates anagramming the letters.
'true' anagrammed gives 'ture'.
'na'+'ture'='NATURE'
(Other definitions for nature that I've seen before include "sort of reserve" , "Character, disposition" , "Character, make-up" , "The world with allits features and living things" , "It abhors a vacuum, according to Aristotle" .)