the liver: the large internal organ, named from a root meaning heavy because it is the weightiest of the inner organs
In its plain sense this word names the liver, the large organ tucked below the ribs. Its name comes from the same root as the word for heavy, because the liver is the weightiest of the body's inner organs. The word is ancient and steady: close relatives with the same meaning turn up in Babylonian, Canaanite, Arabic, and other neighboring languages, so its basic sense has never been in doubt.
The liver appears in three different settings in the Hebrew Bible. Most often it is part of a sacrifice: the priests burned a specific part of the animal's liver, along with the kidneys and fat, as a portion set aside for God. In two poetic passages the liver stands for the whole inner person, the deep seat of life and feeling. And in one scene it is the organ a foreign king reads for omens.
That second use can surprise a modern reader. In ancient Israel, as among its neighbors, the liver was one of the inner organs where a person was thought to feel most deeply, much as we speak of the heart today. So when Lamentations says my liver is poured out on the ground, it is describing crushing grief, not a physical injury. Because English keeps its feelings in the heart, this dimension of the word is easy to miss.