This root term is Greek and means "diaphragm", referring specifically to the respiratory diaphragm. Because of the importance to life of the region that includes the respiratory diaphragm, liver, and heart, Greek and Roman physicians saw this area as the seat of emotions, a concept that later evolved to include mental instability, and mind. So, for them the seat or location of the emotional processes was not in the brain, but in the area of conjunction of liver, heart, and respiratory diaphragm.

In the late 1700's, when Franz J. Gall developed a pseudoscience that looked at protuberances in the cranium as predictors of mental capabilities and mental pathologies, he named it [phrenology], or "study of the mind". In fact, look at the word "frenzy" and you will see a variation of the root [-phren-] in it!

Today we use the root term [-phren-] mostly to denote "respiratory diaphragm", although it can be found in medical words such as [schizophrenia] meaning "mind".