
1) Type of arch
Found on
https://www.crosswordclues.com/clue/barrel-vault

A barrel vault, also known as a tunnel vault or a wagon vault, is an architectural element formed by the extrusion of a single curve (or pair of curves, in the case of a pointed barrel vault) along a given distance. The curves are typically circular in shape, lending a semi-cylindrical appearance to the total design. The barrel vault is the simple...
Found on
http://en.wikipedia.org/wiki/Barrel_vault

an architectural element formed by the extrusion of a single curve (or pair of curves, in the case of a pointed barrel vault) along a given distance
Found on
http://en.wikipedia.org/wiki/Glossary_of_architecture

A semicircular roof of stone or timber.
Found on
http://great-castles.com/glossary.php

ceiling or roof consisting of a series of semicylindrical arches. See vault.[4 related articles]
Found on
http://www.britannica.com/eb/a-z/b/24

A vault in the shape of a half barrel split lengthways
Found on
http://www.castles-of-britain.com/glossary.htm

Cylindrical roof.
Found on
http://www.castlesontheweb.com/glossary.html

Cylindrical roof.
Found on
http://www.encyclo.co.uk/local/20018

. Form of vault made up of continuous semicircular or pointed arch.
Found on
http://www.encyclo.co.uk/local/20941

See vault.
Found on
http://www.encyclo.co.uk/local/21532

semicircular (barrel shaped) roof of stone or timber
Found on
http://www.encyclo.co.uk/local/22129

an architectural element formed by the extrusion of an arch along a given distance.
Found on
http://www.encyclo.co.uk/local/22196

Form of vault made up of continuous semicircular or pointed arch.
Found on
http://www.encyclo.co.uk/local/22200

In architecture a barrel vault (Cradle vault, cylindrical vault or wagon vault) is 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 or curved in plan, as around the apse of a church.
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http://www.probertencyclopaedia.com/browse/TB.HTM

a vault forming a half cylinder.
Found on
http://www.translationdirectory.com/glossaries/glossary336.php

In architecture, a ceiling that is in the form of a semicircular vault with a continuous surface. It is the simplest form of a vault. So called because it resembles a barrel that has been cut in half lengthways. Compare with: groin vault.
Found on
http://www.virtualani.org/glossary/index.htm

[
n] - the simplest form of vault
Found on
http://www.webdictionary.co.uk/definition.php?query=barrel%20vault

semicircular (barrel shaped) roof of stone or timber
Found on
https://www.encyclo.co.uk/local/20402
noun the simplest form of vault; a single continuous arch
Found on
https://www.encyclo.co.uk/local/20974
No exact match found.