1. 1. A large, highly vascular lymphoid organ, lying in the human body to the left of the stomach below the diaphragm, serving to store blood, disintegrate old blood cells, filter foreign substances from the blood, and produce lymphocytes.
   2. A homologous organ or tissue in other vertebrates.
2. Obsolete. This organ conceived as the seat of emotions or passions.
3. Ill temper: vent one's spleen.
4. Archaic. Melancholy.
5. Obsolete. A whim; a caprice.

[Middle English splen, from Old French esplen, from Latin splēn, from Greek.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.