Existential uneasiness (5)
I believe the answer is:
angst
'existential uneasiness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for angst that I've seen before include "Terrible butterflies" , "Acute but unspecified feeling of worry" , "Acute, but unspecific, feeling of anxiety" , "uneasiness" , "General feeling of anxiety" .)