Accuser regularly ignored prompt (3)
I believe the answer is:
cue
'prompt' is the definition.
('cue' can be a synonym of 'prompt')
'accuser regularly ignored' is the wordplay.
'regularly ignored' means one should take alternating letters.
The alternating letters of 'accuser' are 'CUE'.
(Other definitions for cue that I've seen before include "Actor's line to remind another" , "Signal (to actor)" , "Snooker rod" , "Reminder to do something" , "Actor's words" .)