hour of the Boar; around 10 PM
Archaic term from the traditional Japanese temporal system. Refers to the double-hour period associated with the Boar (亥), roughly 9–11 PM or 10 PM–12 AM depending on the era.
In the Edo period, the hour of the Boar referred to the late-night time slot.
Compound of 亥 (い, 'Boar', the twelfth sign of the Chinese zodiac) and 刻 (こく, 'time period'). The term follows the traditional East Asian timekeeping system where each day was divided into twelve double-hour periods named after the zodiac animals.