Come in from barren terrain (5)
I believe the answer is:
'come in' is the definition.
'from barren terrain' is the wordplay.
'from' indicates the answer is hidden within the clue.
'ENTER' can be found hidden inside 'barren terrain'.
(Other definitions for enter that I've seen before include "Infiltrate" , "Gain admission" , "Come/go in" , "Record (in a log)" , "Pierce" .)