tsuitachi

Tsuitachi is the Japanese term for the first day of the month. It is traditionally written with the kanji 一日 and read ついたち when referring to the date. The same kanji can also be read いちにち to mean “one day” or a duration, so context distinguishes between the date and a length of time.

In the Japanese date system, several days have special readings, and the first day is one of the most notable irregular forms. The 1st is read tsuitachi, while the 2nd through the 10th have distinct readings such as futsuka for the 2nd or mikka for the 3rd. Other recurring forms include juuyokka for the 14th and hatsuka for the 20th. These conventional readings are used when stating calendar dates, for example 三月ついたち (みつき? actually さんがつついたち) meaning March 1st, or 二月ついたち for February 1st.

Usage and context: tsuitachi is used in everyday language to indicate the date on the first day of the month. It appears in calendars, official documents, and spoken Japanese when identifying the monthly start. It is distinct from using 一日 to mean a full day or a duration, where the reading would be ichinichi or ichinichijū in phrases like 一日中 (ichinichijū, all day).

See also: calendar terminology in Japanese; the system of irregular day readings (futsuka, mikka, yokka, etc.).