Source : Webster's Revised Unabridged Dictionary (1913)

Sacrament \Sac"ra*ment\, n. [L. sacramentum an oath, a sacred
   thing, a mystery, a sacrament, fr. sacrare to declare as
   sacred, sacer sacred: cf. F. sacrement. See {Sacred}.]
   1. The oath of allegiance taken by Roman soldiers; hence, a
      sacred ceremony used to impress an obligation; a solemn
      oath-taking; an oath. [Obs.]

            I'll take the sacrament on't.         --Shak.

   2. The pledge or token of an oath or solemn covenant; a
      sacred thing; a mystery. [Obs.]

            God sometimes sent a light of fire, and pillar of a
            cloud . . . and the sacrament of a rainbow, to guide
            his people through their portion of sorrows. --Jer.
                                                  Taylor.

   3. (Theol.) One of the solemn religious ordinances enjoined
      by Christ, the head of the Christian church, to be
      observed by his followers; hence, specifically, the
      eucharist; the Lord's Supper.

   Syn: {Sacrament}, {Eucharist}.

   Usage: Protestants apply the term sacrament to baptism and
          the Lord's Supper, especially the latter. The R. Cath.
          and Greek churches have five other sacraments, viz.,
          confirmation, penance, holy orders, matrimony, and
          extreme unction. As sacrament denotes an oath or vow,
          the word has been applied by way of emphasis to the
          Lord's Supper, where the most sacred vows are renewed
          by the Christian in commemorating the death of his
          Redeemer. Eucharist denotes the giving of thanks; and
          this term also has been applied to the same ordinance,
          as expressing the grateful remembrance of Christ's
          sufferings and death. ``Some receive the sacrament as
          a means to procure great graces and blessings; others
          as an eucharist and an office of thanksgiving for what
          they have received.'' --Jer. Taylor.

Sacrament \Sac"ra*ment\, v. t.
   To bind by an oath. [Obs.] --Laud.

Source : WordNet®

sacrament
     n : a formal religious act conferring a specific grace on those
         who receive it; the Protestant sacraments are baptism and
         the Lord's Supper; in the Roman Catholic Church and the
         Eastern Orthodox Church there are seven traditional rites
         accepted as instituted by Jesus: baptism and confirmation
         and Holy Eucharist and penance and holy orders and
         matrimony and extreme unction