Bottom, come up (4)
I believe the answer is:
rear
I believe this clue is a double definition.
'bottom' is the first definition.
('rear' can be a synonym of 'bottom')
'come up' is the second definition.
(thesaurus)
(Other definitions for rear that I've seen before include "Hitchcock film set in one room" , "what can be brought up, finally" , "Bring up - back end" , "Raise - back" , "Bring up (children)" .)