Girl in Isle of Man’s peculiar way of speaking (5)

I believe the answer is:

idiom

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'way of speaking' is the definition.
(I've seen this in another clue)

'girl in isle of man's' is the wordplay.
'girl' becomes 'Di' (short for Diane or Diana).
'in' indicates putting letters inside.
'isle of man' becomes 'iom'.
'di' placed into 'iom' is 'IDIOM'.

'peculiar' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for idiom that I've seen before include "Linguistic peculiarity" , "Vocabulary characteristic of a specific group" , "Special linguistic usage" , "Characteristic language of people or group" , "Colloquialism" .)

I've seen this clue in The Times.

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