Be contiguous with (4)
I believe the answer is:
abut
'be contiguous with' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for abut that I've seen before include "Adjoin, border" , "Impinge" , "Adjoin -- 19 (rev)" , "Lie adjacent to" , "Of building or land, end or lean against" .)