The Collaborative International Dictionary of English v.0.48:

Ark \Ark\ ([aum]rk), n. [OE. ark, arke, arche, AS. arc, earc,
   earce, fr. L. arca, fr. arcere to inclose, keep off; akin to
   Gr. 'arkei^n to keep off.]
   1. A chest, or coffer. [Obs.]
      [1913 Webster]

            Bearing that precious relic in an ark. --Spenser.
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   2. (Jewish Hist.) The oblong chest of acacia wood, overlaid
      with gold, which supported the mercy seat with its golden
      cherubs, and occupied the most sacred place in the
      sanctuary. In it Moses placed the two tables of stone
      containing the ten commandments. Called also the Ark of
      the Covenant.
      [1913 Webster]

   3. The large, chestlike vessel in which Noah and his family
      were preserved during the Deluge. --Gen. vi. Hence: Any
      place of refuge.
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   4. A large flatboat used on Western American rivers to
      transport produce to market.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Ark of the Covenant
    n 1: (Judaism) sacred chest where the ancient Hebrews kept the
         two tablets containing the Ten Commandments [syn: Ark,
         Ark of the Covenant]