Both Uses

idiom
in
Crediting Poetry, by Seamus Heaney
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The child in the bedroom, listening simultaneously to the domestic idiom of his Irish home and the official idioms of the British broadcaster while picking up from behind both the signals of some other distress, that child was already being schooled for the complexities of his adult predicament, a future where he would have to adjudicate among promptings variously ethical, aesthetical, moral, political, metrical, sceptical, cultural, topical, typical, post-colonial and, taken all together, simply impossible.†
The child in the bedroom, listening simultaneously to the domestic idiom of his Irish home and the official idioms of the British broadcaster while picking up from behind both the signals of some other distress, that child was already being schooled for the complexities of his adult predicament, a future where he would have to adjudicate among promptings variously ethical, aesthetical, moral, political, metrical, sceptical, cultural, topical, typical, post-colonial and, taken all together, simply impossible.†
*

Definitions:

(1) (idiom)
a way of putting things that is characteristic of a specific group of people

An idiom typically refers to an expression whose meaning cannot be inferred from the meanings of the words that make it up (as in "feeling under the weather"). It can also refer to a particular artistic style.
(2) (meaning too rare to warrant focus)