The Collaborative International Dictionary of English v.0.48:

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.]
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            I'll take the sacrament on't.         --Shak.
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   2. The pledge or token of an oath or solemn covenant; a
      sacred thing; a mystery. [Obs.]
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            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.
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   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.
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   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.
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The Collaborative International Dictionary of English v.0.48:

Sacrament \Sac"ra*ment\, v. t.
   To bind by an oath. [Obs.] --Laud.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sacrament
    n 1: a formal religious ceremony conferring a specific grace on
         those who receive it; the two Protestant ceremonies 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

The Devil's Dictionary (1881-1906):

SACRAMENT, n.  A solemn religious ceremony to which several degrees of
authority and significance are attached.  Rome has seven sacraments,
but the Protestant churches, being less prosperous, feel that they can
afford only two, and these of inferior sanctity.  Some of the smaller
sects have no sacraments at all -- for which mean economy they will
indubitable be damned.