一六いちろく

1. 1(rolling) a 1 and a 6 (with two dice) Translated by Jiyomi
2. 2dice gambling
3. 3(armed) robbery ; mugging
4. 4Edo 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)

JMdict entry 2851011. Source and licence.