21日にじゅういちにちにじゅういちにちCommon wordMeanings1noun21st day of the monthUsed to specify the 21st day of any month in dates.会かい議ぎは21日にちに行おこなわれます。The meeting will be held on the 21st.2noun21 daysIndicates a duration of 21 days. Often used with counters or in expressions of time span.