Circuitous route round the perimeter (5)
I believe the answer is:
outer
'round the perimeter' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'circuitous route' is the wordplay.
'circuitous' indicates an anagram.
'route' anagrammed gives 'OUTER'.
Can you help me to learn more?
(Other definitions for outer that I've seen before include "Surrounding" , "Archer's shot" , "On the periphery" , "External; peripheral" , "Objective" .)