Push out one’s lips (4)
I believe the answer is:
pout
'push out one's lips' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pout that I've seen before include "Express sulks with lips" , "Moue - sulk" , "show sulkiness" , "Push lips out as sign of annoyance" , "Push out one's lips" .)