means A backless seat for one person, typically perched on three or four legs — or, in medical usage, a piece of feces passed from the bowels.

from From Old English 'stol,' a word for a seat or throne, related to German 'Stuhl' and a distant cousin of words built on the root meaning 'to stand.' For centuries a stool was simply where you sat. The unglamorous bathroom sense arrived later by way of the 'close-stool' or 'stool of ease' — a chamber-pot disguised as a seat — so that 'stool' came to name not just the seat but what was deposited there.