Benedictus

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A canticle that begins Benedictus Dominus Deus Israel (“Blessed be the Lord God of Israel”).
• noun A canticle that begins Benedictus qui venit in nomine Domini (“Blessed is he that cometh in the name of the Lord”) that forms the end of the Sanctus in the Roman Catholic Mass.
• noun A musical setting for either of these canticles.

from The Century Dictionary.

• noun The short canticle or hymn, also distinctively called the Benedictus qui venit, beginning in Latin “Benedictus qui venit in nomine Domini,” and in English “Blessed is He that cometh in the name of the Lord,” preceded and followed by “Hosanna in Excelsis,” that is, “Hosanna in the highest,” which is usually appended in the Roman Catholic mass to the Sanetus, from Psalm cxviii. 26, Luke xix. 38, etc.
• noun A musical setting of this canticle, forming a separate movement in a mass.
• noun The canticle or hymn beginning in Latin “Benedictus Dominus Deus Israel,” and in English “Blessed be the Lord God of Israel”; the song of Zacharias, Luke i. 68–71.
• noun A musical setting of this canticle.

from the GNU version of the Collaborative International Dictionary of English.

• noun The song of Zacharias at the birth of John the Baptist (Luke i. 68); -- so named from the first word of the Latin version.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun music Either of two canticles that begin with the Latin word benedictus
• noun music The music that accompanies these canticles