Very keen on adopting speaker’s latest opening notes (5)
I believe the answer is:
intro
'opening notes' is the definition.
(I've seen this in another clue)
'very keen on adopting speaker's latest' is the wordplay.
'very keen on' becomes 'into'.
'adopting' means one lot of letters goes inside another (inserted letters are taken on or adopted).
'latest' suggests the final letters.
The last letter of 'speaker' is 'r'.
'into' enclosing 'r' is 'INTRO'.
(Other definitions for intro that I've seen before include "this may get one started" , "Opening notes" , "Preliminary part" , "First bars of a piece of popular music" , "Beginning (informal)" .)