[quote="SMHW, post:2, topic:228692"]
I don't think it's a matter of propriety but rather of precision.
They are not fully equivalent terms. Since I'm a math person I like to look at the matter with sets. The liturgy (or if you prefer, liturgies) that are the Mass are subsets of the set of all liturgies.
So it is correct to call the Mass "Sunday Liturgy". But it is not so precise as referring to it as Mass since there can be Sunday Liturgies that are not Masses.
I agree, although the term "services" may be even broader. However many Protestants refer to their services as liturgies as well.
"Eucharistic service," O.E. mæsse, from V.L. *messa "eucharistic service," lit. "dismissal," from L.L. missa "dismissal," fem. pp. of mittere "to let go, send," from concluding words of the service, Ite, missa est, "Go, (the prayer) has been sent," or "Go, it is the dismissal."
1550s, "the service of the Holy Eucharist," from M.Fr. liturgie, from L.L. liturgia "public service, public worship," from Gk. leitourgia, from leitourgos "one who performs a public ceremony or service, public servant," from leito- "public" (from laos "people;" cf. leiton "public hall," leite "priestess") + -ergos "that works," from ergon "work" (see urge (v.)). Meaning "collective formulas for the conduct of divine service in Christian churches" is from 1590s.