External route maybe (5)
I believe the answer is:
outer
'external' is the definition.
('outer' can be similar in meaning to 'external')
'route maybe' is the wordplay.
'maybe' is an anagram indicator.
'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" .)