WELLHOLE
Etymology
Noun
wellhole (plural wellholes)
The open space in a floor, to accommodate a staircase.
The open space left beyond the ends of the steps of a staircase.
A cavity which receives a counterbalancing weight in certain mechanical contrivances, and is adapted also for other purposes.
Source: Wiktionary
Well"hole`, n.
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.
2. A cavity which receives a counterbalancing weight in certain
mechanical contrivances, and is adapted also for other purposes. W.
M. Buchanan.
Source: Webster’s Unabridged Dictionary 1913 Edition