meso

The precise word, and it is narrower than you think. Meso is the Eucharistic liturgy: the Catholic Mass, and by extension the equivalent rite in the Orthodox and high Anglican traditions. It is not a synonym for a church service in general. That word is diservo at 2,668 - dio plus servo, worship of God - which covers any act of public worship in any tradition, including a Quaker meeting and a Protestant Sunday service. All mesoj are diservoj; almost no diservoj are mesoj. A course that blurs those two is teaching you to be inaccurate in a domain where people care about accuracy.

It is not a small message. This is the seam-trap of the word. Mesaĝo is a message, and meso sits in front of it looking like a root that -aĝ- was added to. It is not. Mes- and mesaĝ- are two separate borrowed roots that happen to share three letters, and the suffix -aĝ- is not even an Esperanto affix. The two words do share a distant Latin ancestor - mittere, to send, which gives both missa and missaticum - but that is history, not grammar, and nothing in the Esperanto word is cuttable. A Mass is not a little message.

Register and family. This is encyclopedic vocabulary: mesi is not a verb you will need, but celebri meson is the fixed phrase for saying Mass, ĉeesti meson is to attend one, and meslibro is a missal. A funebra meso is a requiem, a noktomeza meso is midnight Mass, and meso is also the musical form - Bach's B minor Meso, which no Esperantist would call a diservo. Esperanto has a long and genuinely odd relationship with religion, from Zamenhof's own Homaranismo to the Catholic and Bahá'í movements that adopted the language early; the Esperanto and religion article, which this chapter ships, is where that story is told.