Gentle reminder (5)
I believe the answer is:
nudge
'gentle reminder' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nudge that I've seen before include "---. ---, wink, wink (Monty Python)" , "Shove" , "A gentle reminder?" , "Jostle" , "Remind, prompt gently" .)