Understand fear Nick! (9)
I believe the answer is:
apprehend
I believe this clue is a triple definition!
'understand' is the first definition.
(apprehending is a kind of understanding)
'fear' is the second definition.
(I've seen this before)
'nick' is the third definition.
(I've seen this before)
(Other definitions for apprehend that I've seen before include "Arrest; perceive" , "nick" , "Fearfully anticipate" , "Detain" , "Arrest (for a crime)" .)