Euchologion is a Greek term that refers to a liturgical book used in Eastern Orthodox Christianity. This book contains various prayers, hymns, and rituals used in the celebration of the Eucharist and other sacraments. There are several synonyms for this term, including Liturgikon, Hieratikon, and Trebnik. Liturgikon is a Greek word that refers to the book used in the celebration of the Divine Liturgy, while Hieratikon is a liturgical book used by Orthodox priests during services. Lastly, Trebnik is a Slavic term that refers to a collection of liturgical texts used in Slavic-speaking Orthodox Churches, which includes prayers for daily use, as well as services for special occasions and saints' days.