Reminder: start to get undressed? (5)
I believe the answer is:
nudge
'reminder' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
(Other definitions for nudge that I've seen before include "Prod gently with elbow" , "Remind, prompt gently" , "Festive entertainment" , "Jog" , "Push gently" .)