'Tis the Season...
"Mass" as part of Roman Catholic ritual, traces its linguistic roots back to the Latin messa, from missa, a past participle form of the Latin verb mittere, which meant "to send, send away, dismiss." Exactly how "send" became connected with the religious service is not perfectly clear*, but this Latin verb mittere is the source for an unusually large set of English words. Admit, emit, commit, omit, submit, transmit, etc., all have noun forms based on miss-: admission, emission, commission, omission, submission, transmission, etc., and keep close to the original sense of "sending." Slightly less obvious are words like promise, compromise, surmise, which show the same forms for nouns and verbs. From the same source we get missile, missive, mission, and missionary; and through a slightly different path, message, messenger, and even mess (hall). (The "mas" of Christmas appears in a few lesser-known holiday names as well, such as Michaelmas.)
Holiday names, going back in cultural tradition, are often obscure with regard to their original meaning. Halloween (October 31), the American (trick-or-treat) form of which seems to be gaining popularity in both Japan and Europe recently, derives originally from the old Celtic festival of Samhain eve. In ancient Britain and Ireland, into Anglo-Saxon times, New Years was November 1, and on the evening before, huge bonfires were set on hilltops to frighten away evil spirits. The souls of the dead were supposed to revisit their homes on this day, and so eventually the association was made with the ghosts, witches, goblins, black cats, fairies, and demons which make up the costumes of many of today's young trick-or-treaters and costume-party-goers.
Previously written Hallow-e'en, the name is a shortened form of All-Hallow-Even, the evening before All Hallows' or All Saints' Day, a Christian holiday celebrated at the same time. "Hallow" comes from the Old English form "haliga" for "holy" (man), "saint," and it also appeared with a Christmas-like ending: All-hallowmas, the festival of all saints.
The return of the spirits of the dead is similarly found in the Japanese holiday of O-bon, also called Bon Matsuri or Urabon (July 13-15 or August 13-15), which honors the spirits of deceased ancestors. They are believed to return to their birthplaces at this time, and so memorial stones are cleaned, community dances performed, and paper lanterns and fires are lit to welcome them and bid them farewell at the end of their visit. The word Urabon probably derives from the Sanskrit Avalambana (All Souls Day), a Buddhist ceremony based on the Avalambana-sutra, which tells the story of Maudgalyayana, a disciple of the Buddha, who secured his mother's release from hell by having monks offer food, drink, and shelter to the spirits of his ancestors.
Easter, which looks like it should be connected to "east," in fact... seems to be. This Christian holiday, with celebrates the resurrection, or rebirth, of Christ, probably takes its English name from an earlier non-Christian holiday for the dawn-goddess Eostre, which was celebrated at the vernal (spring) Equinox, around the same time as Easter. In most other European languages, the word for Easter shows its connection to the last supper, the Jewish Passover ("pesah" in Hebrew), becoming Pâques in French, Pasqua in Italian, Pascua in Spanish, and Pask in Dutch. The actual date varies from year to year, for it is generally the first Sunday after the full moon (the paschal moon) that occurs upon or next after the vernal equinox (around March 21). Many of the associated customs can be traced back to pre-Christian spring festivals: Easter eggs and the Easter bunny (rabbit) could be easily connected with new life, fertility, and the Christian resurrection.
As with Easter and Halloween, the dates of religious holidays (holy-days) are often found to coincide with those of earlier pagan festivals, and to include many of their traditions. In many cases, this was the result of an attempt on the part of religious leaders to facilitate the transition of the people to the new religion: Rather than attempt to enforce a prohibition of the popular older beliefs, they scheduled their new holidays for the same time, and incorporated many of the traditional customs.
*a note from David Klappholz: 'At the end of the Latin mass the priest says "ite, missa est," meaning "Go, you are dismissed." I believe it's quite well accepted that this is the origin of "missa" as the name of the catholic liturgy.'