A Muslim religious calendar is called a takvim. (firstthings.com)
Easter is one of the holiest days in many religious calendars, and if you observe, it's nice to weave touches of spirituality in with your seasonal decor. (bestproducts.com)
The change in my status was brought about largely by the institutionalizing of the Holocaust, both as a field of academic study and as a fixed day of mourning in the Jewish religious calendar: Yom Hashoah, Day of the Holocaust. (religion-online.org)