The spleen is an organ in your body, tucked under your left ribcage, that helps filter your blood and fight infections. It's about the size of your fist and works quietly behind the scenes, removing old or damaged red blood cells and storing white blood cells that attack germs. If you get hit hard in the side during sports, your spleen is one of the organs that could get injured, which is why referees take body blows seriously.

For centuries, people didn't understand what the spleen actually did, but they noticed that when someone seemed grumpy, irritable, or in a bad mood, it often came with discomfort in that area of the body. So spleen became another word for bad temper or spite. When someone “vents their spleen,” they're releasing their anger or frustration. You might hear someone say a critic spewed spleen at a new movie, meaning they expressed harsh, bitter criticism.

The spleen as an organ does important work keeping you healthy. The spleen as a feeling represents the opposite: letting irritation and bitterness take over. Fortunately, unlike venting your spleen in anger, your actual spleen does its job without you even noticing.