Disposition to see the glass as half-empty (9)
I believe the answer is:
pessimism
'disposition to see the glass as half-empty' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pessimism that I've seen before include "Lack of hope" , "The feeling that things will turn out badly" , "General disposition to expect the worst" , "Disposition to always see the glass as half-empty rather than half-full" , "Tendency to take a gloomy view of things" .)