Circuitous route round the perimeter (5)

I believe the answer is:

outer

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'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" .)

I've seen this clue in the Evening Standard.

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