NISAN (; Assyrian, Nisannu):
First ecclesiastical and seventh civil month (Neh. ii. 1; Esth. iii. 7). In the earlier Biblical books it is designated "Ḥodesh ha-Abib" (month of the harvest). It is regarded as a sacred month because, according to a tradition, the continual burnt offering () was established in it ("Be'er Heṭeb" to Shulḥan 'Aruk, Oraḥ Ḥayyim, 429). It is, therefore, not permissible to observe public mourning and public fasts during the twenty-nine days of this month. The Taḥanun in the daily prayers and the "Ḳidḳatka Ẓedeḳ" in the Minḥah service of Sabbath are to be omitted; neither is the "Ẓidduḳ ha-Din" to be recited at a burial (Oraḥ Ḥayyim, l.c.). The Megillat Ta'anit gives the following fast-days in Nisan:
Nisan 1.—In commemoration of the deaths of Nadab and Abihu, the sons of Aaron, Nisan 10.—In commemoration of the death of Miriam, sister of Moses and Aaron. Nisan 26.—Anniversary of the death of Joshua.
On the evening of the 14th of Nisan the Feast of Passover begins; on the 16th, the second day of Passover, the Hebrews offered a sheaf of barley as the first-fruits of the harvest of the current year; and on the same day began the reckoning (Sefirot) of the seven weeks. From the 17th to the 20th are the "middle days," or the "ḥol ha-mo'ed." The 21st and the 22d are the last feast-days of Passover. Nisan coincides, approximately, with the month of April.