Furthest route is diverted (5)
I believe the answer is:
outer
'furthest' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I can't see?
'route is diverted' is the wordplay.
'is diverted' is an anagram indicator (each letter get diverted elsewhere).
'route' with letters rearranged gives 'OUTER'.
Can you help me to learn more?
(Other definitions for outer that I've seen before include "Ring for double scores on a dartboard" , "External kind of route" , "Archer's shot" , "Exterior or external, like space" , "This space is beyond earth's atmosphere" .)