Catechism of the Catholic Church §1328 — excerpt
The inexhaustible richness of this sacrament is expressed in the different names we give it. Each name evokes certain aspects of it. It is called: Eucharist, because it is an action of thanksgiving to God.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.