Personality disorder (8)
I believe the answer is:
neurosis
'personality disorder' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for neurosis that I've seen before include "Mild mental condition" , "Trouble in mind" , "Mild condition such as obsessive behaviour" , "Resinous (anag) -- unspecific personality disturbance" , "So insure against the nervous disorder" .)