A storey below a basement.
More example sentences
- Basically, it outlined that there was a sub-basement far below where they had been that was the actual control center.
- Somehow, he had wandered into the lower part of the James mansion, the sub-basement.
- The finance department will move into the sub-basement of Needles Hall, where co-op used to be.
Definition of sub-basement in:
- The US English dictionary