%wellhole%

n. [ 1913 Webster ]

1. (Arch.) (a) The open space in a floor, to accommodate a staircase. (b) The open space left beyond the ends of the steps of a staircase. [ 1913 Webster ]

2. A cavity which receives a counterbalancing weight in certain mechanical contrivances, and is adapted also for other purposes. W. M. Buchanan. [ 1913 Webster ]