So saying he skipped around, nimbly considering, frankly at the same time apologetic to get on his companion’s right, a habit of his, by the bye, his right side being, in classical idiom, his tender Achilles.
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.