Introductory letter (7)
I believe the answer is:
initial
I believe this is a double definition.
'introductory' is the first definition.
(I've seen this before)
'letter' is the second definition.
(initial is a kind of letter of the alphabet)
(Other definitions for initial that I've seen before include "shortened version of my name" , "Sign" , "Word's first letter" , "First home, corgi, ultimately, wagging tail" , "subscribe, minimally" .)