Source : Webster's Revised Unabridged Dictionary (1913)

Vault \Vault\ (v[add]lt; see Note, below), n. [OE. voute, OF.
   voute, volte, F. vo[^u]te, LL. volta, for voluta, volutio,
   fr. L. volvere, volutum, to roll, to turn about. See
   {Voluble}, and cf. {Vault} a leap, {Volt} a turn, {Volute}.]
   1. (Arch.) An arched structure of masonry, forming a ceiling
      or canopy.

            The long-drawn aisle and fretted vault. --Gray.

   2. An arched apartment; especially, a subterranean room, use
      for storing articles, for a prison, for interment, or the
      like; a cell; a cellar. ``Charnel vaults.'' --Milton.

            The silent vaults of death.           --Sandys.

            To banish rats that haunt our vault.  --Swift.

   3. The canopy of heaven; the sky.

            That heaven's vault should crack.     --Shak.

   4. [F. volte, It. volta, originally, a turn, and the same
      word as volta an arch. See the Etymology above.] A leap or
      bound. Specifically:
      (a) (Man.) The bound or leap of a horse; a curvet.
      (b) A leap by aid of the hands, or of a pole, springboard,
          or the like.

   Note: The l in this word was formerly often suppressed in
         pronunciation.

   {Barrel}, {Cradle}, {Cylindrical}, or {Wagon}, {vault}
      (Arch.), a kind of vault having two parallel abutments,
      and the same section or profile at all points. It may be
      rampant, as over a staircase (see {Rampant vault}, under
      {Rampant}), or curved in plan, as around the apse of a
      church.

   {Coved vault}. (Arch.) See under 1st {Cove}, v. t.

   {Groined vault} (Arch.), a vault having groins, that is, one
      in which different cylindrical surfaces intersect one
      another, as distinguished from a barrel, or wagon, vault.
      

   {Rampant vault}. (Arch.) See under {Rampant}.

   {Ribbed vault} (Arch.), a vault differing from others in
      having solid ribs which bear the weight of the vaulted
      surface. True Gothic vaults are of this character.

   {Vault light}, a partly glazed plate inserted in a pavement
      or ceiling to admit light to a vault below.

Source : WordNet®

groined vault
     n : two barrel vaults intersecting at right angles