undercroft

[ uhn-der-krawft, -kroft ]

/ ˈʌn dərˌkrɔft, -ˌkrɒft /

a vault or chamber under the ground, especially in a church.

Origin of undercroft

Middle English word dating back to 1350–1400; see origin at under, croft¹

Two heavy wooden doors at the entrance leave no doubt as to the purpose for which the undercroft was built.

Bell's Cathedrals: The Cathedral Church of Wells |Percy Dearmer
The canopy is gone, but fragments of it are in the undercroft of the chapter-house.

Bell's Cathedrals: The Cathedral Church of Wells |Percy Dearmer
In the undercroft itself the walls are impregnably thick, the windows narrow, with wide splays.

Bell's Cathedrals: The Cathedral Church of Wells |Percy Dearmer
This crypt or undercroft is on the same level as the floor of the church, and was used as a treasury.

The Cathedrals of Great Britain |P. H. Ditchfield

The ancient history of this undercroft is unknown, and merely a matter for conjecture.

The Old Inns of Old England, Volume II (of 2) |Charles G. Harper

undercroft

/ (ˈʌndəˌkrɒft) /

an underground chamber, such as a church crypt, often with a vaulted ceiling

C14: from croft a vault, cavern, from earlier crofte, ultimately from Latin crypta crypt