
1) Basement of a building 2) Rooms
Found on
https://www.crosswordclues.com/clue/undercroft

1) Crypt
Found on
https://www.crosswordclues.com/clue/undercroft

An undercroft is traditionally a cellar or storage room, often brick-lined and vaulted, and used for storage in buildings since medieval times. In modern usage, an undercroft is generally a ground (street-level) area which is relatively open to the sides, but covered by the building above.{Fact|date=September 2008} == History == While some were us...
Found on
http://en.wikipedia.org/wiki/Undercroft

crypt or vault under a church
Found on
http://phrontistery.info/u.html

• (n.) A subterranean room of any kind; esp., one under a church (see Crypt), or one used as a chapel or for any sacred purpose.
Found on
http://thinkexist.com/dictionary/meaning/undercroft/

plain room under a domestic building of a medieval house or castle most often used as storage
Found on
http://www.castles-of-britain.com/glossary.htm

A vaulted room or crypt, usually beneath a church or chapel.
Found on
http://www.encyclo.co.uk/local/20766

a vaulted chamber below house, castle or church, partially or wholly underground.
Found on
http://www.encyclo.co.uk/local/20935

In architecture an undercroft is a subterranean room of any kind but especially one under a church, or one used as a chapel or for any sacred purpose.
Found on
http://www.probertencyclopaedia.com/browse/TU.HTM

Basement of a building.
Found on
https://www.encyclo.co.uk/local/20434

a vault or chamber under the ground, esp. in a church.
Found on
https://www.infoplease.com/dictionary/undercroft
No exact match found.