köken: From older 二(に)六(ろく)時(じ)中(ちゅう) (nirokujichū, literally “2×6 hours [a day]”), with 二(に)六(ろく) (niroku, “two [times] six”) replaced with 四(し)六(ろく) (shiroku, “four [times] six”) to reflect the change from traditional Japanese timekeeping, with twelve hours a day divided into two groups of six, to modern, Western-derived timekeeping, with 24 hours for each day.