sacrament

1. (Christianity) A sacred act and the attendant ceremony, considered (theology) an outward sign of divine grace, instituted by Jesus Christ.Examples: "Priest: I'm sorry, it's Duncan Dirk Dick. I've just done it. / Father: Well, undo it. / Priest: Undo it? / Father: Yes. / Priest: This is a holy sacrament of the Church, not a bleeding hotel reservation. You can't just undo it."

2. (in particular) The Eucharist.

3. (by extension) Anything regarded as possessing a sacred character or mysterious significance.Examples: "God ſometimes ſent a light of fire, and pillar of a cloud, and the brightneſſe of an Angel, and the luſtre of a ſtar, and the ſacrament of a rainbovve to guide his people thorovv their portion of ſorrovvs, and to lead them through troubles to reſt: […]"; "The dots are easy to connect, because they’re so close together, and because they’re the entry and exit wounds inflicted on US society by the subculture whose sacrament is the gun."broadly

4. (Ancient Rome) The oath of allegiance taken by soldiers in Ancient Rome; hence, any sacred ceremony used to impress an obligation; a solemn oath-taking; an oath.Examples: "I'll take the sacrament on 't."Ancient-Rome