Sharp reminder (6)
I believe the answer is:
prompt
I believe this is a double definition.
'sharp' is the first definition.
(thesaurus)
'reminder' is the second definition.
(thesaurus)
(Other definitions for prompt that I've seen before include "Bring about; done without delay" , "Give hint as to actor who has forgotten lines (6)" , "Bang on" , "Ready" , "effective in expedition" .)