σπλήν

Splḗn in Greek named the organ located in the upper left abdomen. The word is of uncertain further origin. Greek humoral medicine assigned the spleen to black bile (melaina cholé — the root of 'melancholy'). An excess of black bile, stored and produced by the spleen, caused depression, irritability, spite, and what the Elizabethans would call 'the spleen.' The organ became the seat of every unpleasant emotional state.

The connection between the spleen and temperament persisted for two millennia. In Elizabethan English, 'spleen' could mean anger, melancholy, caprice, impulsiveness, or a sudden fit of laughter. Shakespeare used the word for nearly all of these. The organ was a universal emotional explanation — if you felt something dark, your spleen was responsible. The word was diagnosis, location, and emotion simultaneously.

Modern medicine has a more modest view. The spleen filters blood, recycles old red blood cells, and stores white blood cells and platelets. It is part of the immune system, not the emotional system. You can live without a spleen — people who have splenectomies (surgical removal) survive with increased vulnerability to certain infections but no change in temperament. The organ that supposedly ruled emotions turns out to be a blood filter.

The idiom 'to vent your spleen' survives, meaning to express anger or frustration. The word 'splenetic' — meaning irritable, peevish — also survives. Both preserve the ancient belief that the organ generates negative emotions. The belief is false. The idioms are permanent.