Opening statement (8)
I believe the answer is:
preamble
'opening statement' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for preamble that I've seen before include "Introductory or opening statement" , "It starts" , "Introductory explanation" , "Introductory part of document or law" , "Overture" .)