Usual disguise for army scout (9)

I believe the answer is:

customary

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'usual' is the definition.
(similar in meaning)

'disguise for army scout' is the wordplay.
'army scout' anagrams to 'CUSTOMARY'.
However, I am not clear how this is indicated.

Can you help me to learn more?

(Other definitions for customary that I've seen before include "Conventional" , "In accordance with convention" , "Courts may find this usual" , "According to usual practice" , "Normal, usual" .)

I've seen this clue in The Irish Independent.

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