An Oslo bar? (6)

I believe the answer is:

saloon

I'm a little stuck... Click here to teach me more about this clue!

'bar?' is the definition.
(I know that saloon is a type of bar)

'an oslo' is the wordplay.
'an oslo' can be anagrammed to 'SALOON'.
But, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for saloon that I've seen before include "Describing a bar - describing a car" , "An American pub, as in the wild west" , "Large public room" , "Car; public room" , "Bar room" .)

I've seen this clue in the Evening Standard.

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