- an underground chamber, such as a church crypt, often with a vaulted ceiling
WordReference Random House Unabridged Dictionary of American English © 2026
un•der•croft
(un′dər krôft′, -kroft′),USA pronunciation n.
- Architecturea vault or chamber under the ground, esp. in a church.
- 1350–1400; Middle English; see under, croft
Collins Concise English Dictionary © HarperCollins Publishers::
undercroft /ˈʌndəˌkrɒft/ n