Come or go in (5)
I believe the answer is:
enter
I believe this clue is a double definition.
'come' is the first definition.
(thesaurus)
'go in' is the second definition.
(as in entering a building)
(Other definitions for enter that I've seen before include "Fruit drink" , "Enlist, join up" , "cross the threshold" , "Pierce" , "Come or go in" .)