Edo–early Meiji non-working day on dates with 1 or 6
Historical term for a regular holiday observed from the Edo period into the early Meiji era. It fell on the 1st, 11th, 16th, 21st, and 26th of each month—days whose dates, when written in kanji numerals, contain the characters 一 (1) or 六 (6).
During the Edo period, merchant houses often took 一六日 as a day off.
一六日 was a holiday that came around about five times a month.