Obsessive and persistent fear of something (6)
I believe the answer is:
phobia
'obsessive and persistent fear of something' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for phobia that I've seen before include "Irrational hatred" , "Extreme and irrational fear" , "Anxiety disorder" , "Pathological fear" , "Great fear of something" .)