Wellhole

1. n. A cavity which receives a counterbalancing weight in certain mechanical contrivances, and is adapted also for other purposes.
2. n. The open space in a floor, to accommodate a staircase.
3. n. The open space left beyond the ends of the steps of a staircase.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.