Keen on accepting right opening (5)
I believe the answer is:
intro
'opening' is the definition.
(short for introduction)
'keen on accepting right' is the wordplay.
'keen on' becomes 'into' (I've seen this before).
'accepting' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'into' placed around 'r' is 'INTRO'.
(Other definitions for intro that I've seen before include "Brief passage to start a piece of popular music" , "starter" , "First bars of a musical composition" , "Opener" , "Opening bars (abbr)" .)