Our Duncan's tongue (4)

I believe the answer is:

urdu

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

'tongue' is the definition.
(Urdu is a language or tongue)

'our duncan's' is the wordplay.
'URDU' is hidden in amongst the letters.
However, I'm uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for urdu that I've seen before include "Language used in Pakistan, India" , "Pakistani language" , "Sanskrit language" , "speech" , "Form of Hindustani" .)

I've seen this clue in The Daily Express and The Mirror.

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