A·shu·ra 
(ə-shrə)
(ə-shrə)n.
1. The tenth day of Muharram, observed as a holy day of mourning by Shiites on the anniversary of the death of Hussein, grandson of Muhammad.
2. The tenth day of Muharram, observed in Sunni Islam as an optional day of fasting established by Muhammad.
[Arabic 'āšūrā', the tenth day of Muharram kept as a day of fasting by Arabs in pre-Islamic times, Ashura, ultimately (probably via Aramaic *'āsorā) from Hebrew 'āśôr, a set of ten (days, etc.), decade (used in Leviticus to specify the date of Yom Kippur, the tenth day of Tishri), from 'eśer, ten; see ʿśr in the Appendix of Semitic roots.]