At Mass we proclaim, “Hosanna in the highest.” What does Hosanna mean?
"Blessed is he who comes in the name of the Lord! Hosanna in the highest!" (Matt. 21:9) was shouted by the crowds as Jesus entered Jerusalem. The word hosanna is associated with rejoicing. According to the Catholic Encyclopedia:
The general opinion is that of St. Jerome, that the word originated from two Hebrew words of Psalm cxvii (cxviii), 25. This psalm, " Confitemini Domino quoniam bonus," was recited by one of the priests every day during the procession round the altar, during the Feast of Tabernacles, when the people were commanded to "rejoice before the Lord" (Lev. 23:40); and on the seventh day it was recited each time during the seven processions. When the priest reached verses 25–26, the trumpet sounded, all the people, including boys, waved their branches of palms, myrtles, willows, etc., and shouted with the priest the words: O Domine, salvum (me) fac; o Domine, bene prosperare. Benedictus qui venit in nomine Domini! The Hebrew for salvum fac or serva nunc was hoshi’a na. This was repeated so frequently that it became abbreviated into "hosanna."