Where did the word “sacrament” come from?
Often non-Lutherans are bothered by the fact that Lutherans teach there are sacraments. They think that the word “sacrament” is somehow a “Roman Catholic” thing. No, it is simply a “Bible thing,” therefore, “a Christian thing.” I found a nice little summary of where the word “sacrament” comes from.
By the end of third century, Latin had overtaken Greek as the language of common people in the western half of the Roman Empire. Western clergy preached in Latin, western theologians wrote in Latin, and western scholars translated the Bible into Latin. Western Christians heard the sermons, read the writings, and studied the Bible in Latin. The word μυστηριον was a problem. There was no Latin word that corresponded to it. They could have transliterated the Greek word into Latin as mysterium, and they often did that, but that did not solve the problem so much as avoid it, because most Latin-speaking people still had no idea what it meant. So western Christian scholars used the word sacramentum to translate μυστηριον. These scholars included Tertullian, who was one of the earliest Latin theologians, and Jerome, who translated the Bible into Latin about a hundred years later.
But where did they get this word and why did they choose it? They borrowed it from the Roman Army. A recruit for the Roman army became a soldier by undergoing a sacramentum. The sacramentum had two parts: the soldier took an oath of office, and the Army branded him behind the ear with the number of his legion. The sacramentum resulted in new responsibilities and new advantages. The soldier acquired the responsibility for conforming to military discipline and obeying military commands. He also acquired social and legal benefits, because living conditions in the Roman Army were very good and veterans received special privileges and benefits. Ancient Latin theologians seized upon sacramentum as the best Latin equivalent of the Greek word mystery when it referred to a church rite, because the church rite is simultaneously spiritual and physical, and because the person who undergoes the sacrament simultaneously receives new responsibilities and a new spiritual status before God.
So that is how the word sacrament came into Christian theology in the west. For many centuries, the secular and the theological uses of the word existed side by side. By the time of the Reformation, it was solely a Christian theological term.