sacramentum

Sacramentum, sacramenti is second declension neuter, from sacro, "to consecrate": literally a thing made sacred. It has had two entirely separate careers.

In Republican Latin it was first the money each party staked in a lawsuit, deposited in a temple and forfeited by the loser, and then the military oath of allegiance. Sacramentum dicere is to be sworn in, sacramento tenebantur is "they were bound by their oath", and neither has anything to do with religion in the modern sense. Then the early Church used it to translate Greek mysterion, and the theological meaning grew until it swallowed the old one. So in Caesar or Livy sacramentum is an oath and reading it as a sacrament is a plain anachronism; in this corpus, which is largely ecclesiastical, the reverse mistake is the likelier one.