Area existing before motorway (5)
I believe the answer is:
realm
'area' is the definition.
(synonyms)
'existing before motorway' is the wordplay.
'existing' becomes 'real' (similar in meaning).
'before' says to put letters next to each other.
'motorway' becomes 'm'.
'real'+'m'='REALM'
(Other definitions for realm that I've seen before include "where ruler holds sway?" , "Lamer (anag.)" , "Royal domain" , "field of study" , "Kingdom's" .)