crypt
n.a stone room under the floor of a church where people are buried. It is usually dark, cold, and quiet.
n.an underground room or vault, typically beneath the main floor of a church, used as a chapel or burial place.
“The old church has a dark crypt beneath the altar.”
“Visitors can descend the narrow stone stairs to see the ancient tombs located in the cathedral's crypt.”
“The architect designed the cathedral with a sprawling crypt to house the remains of the city's historical figures, ensuring the foundation remained structurally sound despite the hollow chambers.”
Learned borrowing from Latin crypta (“vault”), from Ancient Greek κρυπτός (kruptós, “hidden”). Doublet of grotto.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.