Definition of: spleen

(splēn) noun Anat.
1. A highly vascular, flattened, ductless organ found near the stomach of most vertebrates, which effects certain modifications in the blood. ♦ Collateral adjective: lienal.
2. This organ regarded as the seat of various emotions.
3. Ill temper; spite-fulness: to vent one's spleen.
4. Archaic Lowness of spirits; melancholy; hypochondria.
5. Obs. Mode or state of mind; also, caprice; a fit of pique.
6. Obs. Violent mirth. [<L splen <Gk. splēn]
—spleen′ish adjective
—spleen′y adjective