Word Origin & History
O.E. osanna, from Heb. hosha'na, probably a shortening of hoshi'ah-nna "save, we pray" (cf. Psalms cxviii.25), from imper. of y-sh- (cf. yeshua "salvation, deliverance, welfare") + emphatic particle -na. Originally an appeal for deliverance; used in Christian Church as an ascription of praise, because
when Jesus entered Jerusalem this was shouted by Galilean pilgrims in recognition of his messiahhood (Matt. xxi.9, 15, etc.).