1. Rosh Hashanah - Noun
2. Rosh Hashanah - Proper noun
(Judaism) a solemn Jewish feast day celebrated on the 1st or 1st and 2nd of Tishri; noted for the blowing of the shofar
Source: WordNetAny adjustments needed to postpone Rosh Hashanah must be made to the adjustable months in the year that precedes the year of which the Rosh Hashanah will be the first day. Source: Internet
For calendar descriptions in general the day begins at 6 p.m., but for the purpose of determining Rosh Hashanah, a molad occurring on or after noon is treated as belonging to the next day (the first deḥiyyah). Source: Internet
However, because of the holiday rules, Rosh Hashanah cannot fall on a Sunday, Wednesday, or Friday, so if TM2 is one of those days, Rosh Hashanah in year 2 is postponed by adding one day to year 1 (the second deḥiyyah). Source: Internet
If the application of deḥiyyah molad zaken would place Rosh Hashanah on one of these days, then it must be postponed a second day. Source: Internet
If TM1 is Sunday, Wednesday or Friday, Rosh Hashanah in year 1 is postponed, so year 1 is not the maximum length. Source: Internet
In a regular (kesidran) year Kislev has 30 days, but because of the Rosh Hashanah postponement rules, in some years it can lose a day to make the year a "short" (chaser) year. Source: Internet