(a) an aperture for access to the well of a ship (see sense 8a); (b) a shaft or opening in a building for a lift, elevator, escalator, etc.

(originally) a tube inserted into a well shaft, through which water or oil is extracted; (later) the inner casing in a driven well.

the action or an act of making a well by drilling into the ground; (also) a well shaft.

A vertical hole or shaft in the ground; spec. the shaft or borehole of a well.

In singular and plural. Apparently: the main body of a well or shaft.