undercroft
noun
un·der·croft ˈən-dər-ˌkrȯft 
: a subterranean room
especially : a vaulted chamber under a church
Example Sentences
Recent Examples on the Web Dine-in option on March 4, March 11 and March 18 in the undercroft. 
Luann Gibbs, The Enquirer, 1 Mar. 2022 First, officials requested rooms with more space at existing locations where possible, such as moving voting from a church’s undercroft and into its gym. Duard Headley, The Enquirer, 2 Nov. 2020 The café is located in Edward III's medieval undercroft (a cellar or storage room), which has been used for centuries as the estate's wine cellar. Annie Goldsmith, Town & Country, 10 Mar. 2020 New exhibits will be added, and visitors will be able to see the massive pilings and foundation that support the memorial in its undercroft. Michael E. Ruane, Washington Post, 14 June 2018 While the Abbey had a smaller museum in the 11th-century undercroft off the cloisters until 2015, the new gallery offers space for four times as many objects for a total of 300. Dana Rose Falcone, PEOPLE.com, 30 May 2018
Luann Gibbs, The Enquirer, 1 Mar. 2022 First, officials requested rooms with more space at existing locations where possible, such as moving voting from a church’s undercroft and into its gym. Duard Headley, The Enquirer, 2 Nov. 2020 The café is located in Edward III's medieval undercroft (a cellar or storage room), which has been used for centuries as the estate's wine cellar. Annie Goldsmith, Town & Country, 10 Mar. 2020 New exhibits will be added, and visitors will be able to see the massive pilings and foundation that support the memorial in its undercroft. Michael E. Ruane, Washington Post, 14 June 2018 While the Abbey had a smaller museum in the 11th-century undercroft off the cloisters until 2015, the new gallery offers space for four times as many objects for a total of 300. Dana Rose Falcone, PEOPLE.com, 30 May 2018 Word History
Etymology
Middle English, from under + crofte crypt, from Middle Dutch, from Medieval Latin crupta, from Latin crypta — more at crypt
First Known Use
14th century, in the meaning defined above