What does "stool" mean?

Additional senses

1. 2.A seat used in evacuating the bowels; hence, an evacuation; a discharge from the bowels.
2. 3.A stool pigeon, or decoy bird. [U. S.]
3. 4.(Naut.) A small channel on the side of a vessel, for the dead-eyes of the backstays. Totten.
4. 5.A bishop's seat or see; a bishop-stool. J. P. Peters.
5. 6.A bench or form for resting the feet or the knees; a footstool; as, a kneeling stool.
6. 7.Material, such as oyster shells, spread on the sea bottom for oyster spat to adhere to. [Local, U.S.] Stool of a window, or Window stool (Arch.), the flat piece upon which the window shuts down, and which corresponds to the sill of a door; in the United States, the narrow shelf fitted on the inside against the actual sill upon which the sash descends. This is called a window seat when broad and low enough to be used as a seat. Stool of repentance, the cuttystool. [Scot.] -- Stool pigeon, a pigeon used as a decoy to draw others within a net; hence, a person used as a decoy for others.