一六日いちろくび

1. 1Edo period to early Meiji non-working day falling on all days of the month with a 1 or a 6 in it (when written in kanji numerals, i.e. the 1st, 11th, 16th, 21st and 26th days of the month) Translated by Jiyomi

JMdict entry 2851019. Source and licence.