No Slovenian capital! (4)

I believe the answer is:

oslo

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

'capital' is the definition.
(capital of Norway)

'no slovenian' is the wordplay.
'OSLO' is hidden in amongst the letters.
But, I'm uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for oslo that I've seen before include "Northern city" , "Capital of Norway" , "Scandinavian city" , "Norwegian chief port" , "Norway's capital city" .)

I've seen this clue in the Evening Standard.

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