The noun STOOL has 4 senses: 1. a simple seat without a back or arms. 2. solid excretory product evacuated from the bowels. 3. (forestry) the stump of a tree that has been felled or headed for the production of saplings. 4. a plumbing fixture for defecation and urination. Familiarity information: STOOL used as a noun is uncommon.