External route diverted (5)
I believe the answer is:
outer
'external' is the definition.
(similar in meaning)
'route diverted' is the wordplay.
'diverted' indicates an anagram (each letter get diverted elsewhere).
'route' with letters rearranged gives 'OUTER'.
(Other definitions for outer that I've seen before include "Ring furthest from the bullseye" , "Route (anag.)" , "Exterior or external, like space" , "On the periphery" , "Surrounding" .)