What is "vault light"

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:

   1. (Man.) The bound or leap of a horse; a curvet.

   2. 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 vault, Cradle vault, Cylindrical vault, 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.