Pub on map is keeping to route (4)
I believe the answer is:
path
'route' is the definition.
(synonyms)
'pub on map is keeping to' is the wordplay.
'pub on map' becomes 'ph' (abbreviation for public house seen on maps).
'is keeping' means one lot of letters goes inside another.
'to' becomes 'at' (I am not sure about this - if you are sure you should believe this answer much more).
'ph' enclosing 'at' is 'PATH'.
(Other definitions for path that I've seen before include "Line of travel" , "Will's go" , "Course of action; track" , "Pavement" , "Walkway" .)