Teenager's not entirely happy out here (5)
I believe the answer is:
youth
'teenager's' is the definition.
(I've seen this before)
'not entirely happy out here' is the wordplay.
'not entirely' indicates a hidden word.
'YOUTH' is hidden within 'happy out here'.
(Other definitions for youth that I've seen before include "Youngster" , "Salad days" , "Teenager" , "7" , "Children" .)