Indifference — sputum (6)
I believe the answer is:
phlegm
This clue is a double definition.
'indifference' is the first definition.
(I know that indifference can be written as phlegm)
'sputum' is the second definition.
(I know that sputum can be written as phlegm)
(Other definitions for phlegm that I've seen before include "Composure" , "Mucus - self-possession" , "Coolness" , "Mucus - stolidity" , "Imperturbable stolidity" .)