souterrain
An underground chamber or passage sometimes used as a store, especially one associated with Iron Age settlements.
Now when my son saw that I separated them, he secretly built this souterrain and furnished it and transported to it victuals, even as thou seest; and, when I had gone out a-sporting, came here with his sister and hid from me.
Where it comes from
From French souterrain, from sous (“under”) + terrain (“ground”).
Adapted from the Wiktionary entry souterrain (CC BY-SA 4.0).