So that there are instances among them of men, who, named with Scripture names—a singularly common fashion on the island—and in childhood naturally imbibing the stately dramatic thee and thou of the Quaker idiom; still, from the audacious, daring, and boundless adventure of their subsequent lives, strangely blend with these unoutgrown peculiarities, a thousand bold dashes of character, not unworthy a Scandinavian sea-king, or a poetical Pagan Roman.
There are no more uses of "idiom" in the book.
Show samples from other sources
I said, using one of my favorite Siaru idioms.
Patrick Rothfuss -- The Name of the Wind
The words he uses are the idioms of popular songs and poems in the newspaper.