External route maybe (5)
I believe the answer is:
outer
'external' is the definition.
(similar in meaning)
'route maybe' is the wordplay.
'maybe' indicates anagramming the letters.
'route' anagrammed gives 'OUTER'.
(Other definitions for outer that I've seen before include "External; part of archery target" , "On the periphery" , "Objective" , "Archer's shot" , "External; peripheral" .)