Nonchalance in a sense is affected (8)
I believe the answer is:
easiness
'nonchalance' is the definition.
(I've seen this before)
'a sense is affected' is the wordplay.
'affected' indicates an anagram.
'a'+'sense'+'is'='asenseis'
'asenseis' anagrammed gives 'EASINESS'.
'in' acts as a link.
(Other definitions for easiness that I've seen before include "Facile quality" , "Lack of difficulty" , "Nonchalance" .)