(music) A mass, in the sense of a composition setting several sung parts of the liturgic service (most often chosen from the ordinary parts Kyrie, Gloria, Credo, Agnus Dei and/or Sanctus) to music, notably when the text in Latin is used (as long universally prescribed by Rome)
Wiktionary
Origin of Missa
From the Latin phrase Ite, missa est (“Go, it is the dismissal/sending”), reinterpreted as naming the ceremony: "Go, it is the Mass", or "Go, the Mass is over"; from perfect passive participle missus (“dismissal, sending”), from mittere (“send”, verb).
