Gentle poke (5)
I believe the answer is:
'gentle poke' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nudge that I've seen before include "Give a reminder" , "Jostle" , "Gentle poke with elbow" , "Poke gently with elbow" , "Remind, prompt gently" .)