What Aramaic term describes Rosh Hashanah's two days as 'one long day'?

The Aramaic term for Rosh Hashanah’s two days as “one long day” is Yoma Arichtah.

Yoma Arichtah means “one long day” or “a single extended day.” The expression describes the special status traditionally given to the first two days of Tishrei, which are observed together even though they fall on two calendar dates.

The practice developed from uncertainty about the date of the new moon. In the ancient system, communities outside Jerusalem could not always receive timely confirmation of when the month began, so an extra festival day was observed. Rosh Hashanah retained this two-day observance even in places where other festivals may be observed for only one day in Israel.

Yoma Arichtah does not mean that the holiday literally lasts one 48-hour calendar day. It is a legal and religious description with practical implications in halakhah. The phrase is also easy to confuse with Yom Tov Sheni, the broader concept of a second festival day observed in many Diaspora communities; Yoma Arichtah is specifically associated with the two days of Rosh Hashanah.