Strike fear into close friend concealing identity (10)
I believe the answer is:
intimidate
'strike fear into' is the definition.
(I've seen this before)
'close friend concealing identity' is the wordplay.
'close friend' becomes 'intimate' (I've seen this before).
'concealing' is an insertion indicator.
'identity' becomes 'id' (I've seen this in other clues).
'intimate' going around 'id' is 'INTIMIDATE'.
(Other definitions for intimidate that I've seen before include "Cow" , "Strike fear into" , "Scare" , "Bully" , "Frighten" .)