Share a side with (4)
I believe the answer is:
abut
'share a side with' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for abut that I've seen before include "Cease (from activity)" , "Be next to -- share a boundary" , "Meet" , "Tuba (anag)" , "End or lean against, say a building" .)