Shock line included in note (4)
I believe the answer is:
jolt
'shock' is the definition.
(thesaurus)
'line included in note' is the wordplay.
'line' becomes 'l'.
'included in' means one lot of letters goes inside another.
'note' becomes 'jot' (jot is a kind of note**).
'l' inserted within 'jot' is 'JOLT'.
(Other definitions for jolt that I've seen before include "Shock, jerk" , "Knock sharply so as to dislodge" , "Sudden shock" , "A sudden jar" , "Jostle; shock" .)