Old chap — one from SW Asian country (5)

I believe the answer is:

omani

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'sw asian country' is the definition.
I can't tell whether this defines the answer.

'old chap one' is the wordplay.
'old' becomes 'o' (abbreviation).
'chap' becomes 'man' (chap can mean a man).
'one' becomes 'i' (Roman numeral).
'o'+'man'+'i'='OMANI'

'from' acts as a link.

Can you help me to learn more?

(Other definitions for omani that I've seen before include "one from the Middle East" , "Middle East national" , "Gulf native" , "M East person" , "One from Muscat" .)

I've seen this clue in The Times.

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