εὐχαριστία

Greek eukharistía combined eu (good, well) with kháris (grace, favor, gratitude). The word simply meant thanksgiving. In secular Greek, you might express eukharistía for a gift, a favor, or a meal. The word became attached to the Christian ritual of bread and wine because Jesus, at the Last Supper, 'gave thanks' (eucharistēsas in the Greek of Luke 22:19) before breaking the bread. The act of thanksgiving named the sacrament.

The early Church used several names for the ritual: the Lord's Supper (Kyriakon Deipnon), the Breaking of Bread (Klasis tou Artou), and the Eucharist. By the second century, Eucharist was becoming standard. Ignatius of Antioch used it around 110 CE. Justin Martyr described the Eucharist in detail around 155 CE. The word settled into Christian vocabulary within a century of the events it commemorated.

Theological disputes over the Eucharist split Christianity repeatedly. Transubstantiation — the Catholic doctrine that the bread and wine literally become the body and blood of Christ — was formally defined at the Fourth Lateran Council in 1215. Luther rejected transubstantiation but affirmed real presence. Zwingli argued the ritual was purely symbolic. Calvin took a middle position. The word Eucharist names a ritual that Christians cannot agree on the meaning of. The thanksgiving is unanimous. The theology is not.

Different Christian traditions use different words. Catholics say 'the Eucharist' or 'Holy Communion.' Protestants often say 'Communion' or 'the Lord's Supper.' Eastern Orthodox say 'the Divine Liturgy.' The word Eucharist — specifically Greek, specifically Catholic in tone — carries denominational weight. Using it signals a certain theological tradition. The word for thanksgiving became a shibboleth.