SIDDUR AND MAḤZOR. The siddur and the maḥzor (pl., siddurim and maḥzorim) are the prayer books used in Jewish public worship. The term siddur ("order"; from the Hebrew root sdr, "order, arrange") signifies an order of prayer and generally denotes weekday and Sabbath liturgy. The term maḥzor ("cycle"; from the root ḥzr, "return, come around again") denotes the annual cycle of prayer for holidays that come but once a year; the maḥzor is therefore usually subdivided nowadays into separate volumes for each holiday: that is, the maḥzor for Passover, Sukkot, or Shavuʿot (the Pilgrimage Festivals) or for Roʾsh ha-Shanah or Yom Kippur (the Days of Awe, or High Holy Days). Surprisingly, the determination of a standardized text for these volumes is a relatively late phenomenon and, in fact, is still...