Subbasement (noun)

A floor or level of a building located below the basement.

Origin:

From 'sub-' meaning 'below' and 'basement', referring to a level below the basement.

Examples:

1. The subbasement was used for storage and as a laundry room.
2. The subbasement was damp and musty, but it was the perfect place for a home gym.
3. The subbasement had been converted into a recreational room for the children.
4. The subbasement was a secure location for the valuable paintings.
5. She was surprised to find a fully equipped kitchen in the subbasement.