Barrier with everything (4)
I believe the answer is:
wall
'barrier' is the definition.
(a wall acts as a barrier)
'with everything' is the wordplay.
'with' becomes 'w' (abbreviation).
'everything' becomes 'all' (all things).
'w'+'all'='WALL'
(Other definitions for wall that I've seen before include "See 14" , "Brick or stone barrier" , "Brick fence" , "Boundary of brick or stone" , "Separator of Pyramus and Thisbe" .)