sac

A sac is a pouch-like part of a plant, animal, or body. It is usually a small space made of thin tissue or membrane that holds or protects something. Think of the amniotic sac around a developing baby, the tiny air sacs in the lungs, or an egg sac that holds eggs. The idea is simple: it is a natural pocket that contains something important.

Fundamentally, a sac is a small pouch, bag, or enclosed space that holds, stores, or protects something. The word appears most often in biology, medicine, and anatomy, where it refers to a natural structure rather than an ordinary container. You might read about the amniotic sac, the tiny air sacs in the lungs, a tear sac near the eye, or an egg sac made by an insect or spider.

The idea can also extend to plants and other living things. In botany, for example, a flower may contain pollen sacs, and in medicine, doctors may describe a fluid-filled sac or a membrane around an organ. In all of these cases, the image is the same: a soft or enclosed pocket with a clear job to do.

Less often, the word can describe any similar enclosed pocket or chamber when the shape or function matters more than the material. Whether it is protecting new life, holding fluid, or carrying pollen, a sac suggests a small, protective container built by nature or described in scientific terms.