The Collaborative International Dictionary of English v.0.48:
Stool \Stool\, n. [AS. st[=o]l a seat; akin to OFries. & OS.
st[=o]l, D. stoel, G. stuhl, OHG. stuol, Icel. st[=o]ll, Sw.
& Dan. stol, Goth. st[=o]ls, Lith. stalas a table, Russ.
stol'; from the root of E. stand. [root]163. See Stand, and
1. A single seat with three or four legs and without a back,
made in various forms for various uses.
2. A seat used in evacuating the bowels; hence, an
evacuation; a discharge from the bowels.
3. A stool pigeon, or decoy bird. [U. S.]
4. (Naut.) A small channel on the side of a vessel, for the
dead-eyes of the backstays. --Totten.
5. A bishop's seat or see; a bishop-stool. --J. P. Peters.
6. A bench or form for resting the feet or the knees; a
footstool; as, a kneeling stool.
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.