The word "Eucharist" comes from the Greek word "eukaristos," which means "grateful" and is usually translated as "thanksgiving." It now refers to the sacrament of the Lord's Supper, in which bread and which becomes the body and blood of Christ. Eucharist has become essentially synonymous with "Communion" or "Holy Communion.
The earliest written account of of the institution of the Eucharist is contained in Paul's letter to the Corinthians, written in the spring of the year 55 AD. The Didache, a church document from the end of the first century refers to the Eucharist by name, gives explicit instructions for the form of the prayers, and cautions, "Let no one eat or drink of your Eucharist except those baptized in the name of the Lord." The earliest complete Eucharistic prayer is in a document form 225 AD identified with Hippolytus. It is identical (almost word for word) to the Eucharistic prayer used today by nearly all Catholic and orthodox churches.