Identify Crown Dependency’s dialect (5)

I believe the answer is:

idiom

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'dialect' is the definition.
(I know that dialect can be written as idiom)

I cannot understand how the remainder of the clue works.

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(Other definitions for idiom that I've seen before include "Peculiarity of phrase in a language" , "Expression that does not make literal sense" , "Use of words" , "Vocabulary characteristic of a specific group" , "Dialect, vernacular" .)

I've seen this clue in The Times.

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