Quick reminder (6)
I believe the answer is:
prompt
I believe this is a double definition.
'quick' is the first definition.
(synonyms)
'reminder' is the second definition.
(I've seen this before)
(Other definitions for prompt that I've seen before include "Remind (actor) of lines" , "Quick, without delay" , "Cue given to a performer" , "Jog the memory" , "Give hint as to actor who has forgotten lines (6)" .)