The word Mass (missa) first established itself as the general designation for the Eucharistic Sacrifice in the West after the time of Pope Gregory the Great (d. 604), the early Church having used the expression the "breaking of bread" (fractio panis) or "liturgy" (Acts 13:2, leitourgountes); the Greek Church has employed the latter name for almost sixteen centuries.
There were current in the early days of Christianity other terms;
"The Lord's Supper" (coena dominica),
the "Sacrifice" (prosphora, oblatio),
"the gathering together" (synaxis, congregatio),
"the Mysteries", and
(since Augustine), "the Sacrament of the Altar".
With the name "Love Feast" (agape) the idea of the sacrifice of the Mass was not necessarily connected. Etymologically, the word missa is neither (as Baronius states) from a Hebrew, nor from the Greek mysis, but is simply derived from missio, just as oblata is derived from oblatio, collecta from collectio, and ulta from ultio. The reference was however not to a Divine "mission", but simply to a "dismissal" (dimissio) as was also customary in the Greek rite (cf. "Canon. Apost.", VIII, xv: apolyesthe en eirene), and as is still echoed in the phrase Ite missa est. This solemn form of leave-taking was not introduced by the Church as something new, but was adopted from the ordinary language of the day, as is shown by Bishop Avitus of Vienne as late as A.D. 500 (Ep. 1 in P.L., LIX, 199):
In churches and in the emperor's or the prefect's courts, Missa est is said when the people are released from attendance.
In the sense of "dismissal", or rather "close of prayer", missa is used in the celebrated "Peregrinatio Silvae" at least seventy times (Corpus scriptor. eccles. latinor., XXXVIII, 366 sq.) and Rule of St. Benedict places after Hours, Vespers, Compline, the regular formula: Et missae fiant (prayers are ended). Popular speech gradually applied the ritual of dismissal, as it was expressed in both the Mass of the Catechumens and the Mass of the Faithful, by synecdoche to the entire Eucharistic Sacrifice, the whole being named after the part. The first certain trace of such an application is found in Ambrose (Ep. xx, 4, in P.L. XVI, 995). We will use the word in this sense in our consideration of the Mass in its existence, essence, and causality.
Answer by GlitteribonMom at 3:09 PM on Jul. 24, 2012