Ab·bas·id also Ab·bas·sid 
(ə-băsĭd′, ăbə-sĭd′) or Ab·bas·ide (ə-băsīd′, ăbə-sīd′)
(ə-băsĭd′, ăbə-sĭd′) or Ab·bas·ide (ə-băsīd′, ăbə-sīd′) An Arabic dynasty (750-1258) that expanded the Muslim empire. It was named for al-Abbas (566?-652), paternal uncle of the prophet Muhammad.