What does sac mean?
A sac is a pouchlike structure, especially one found in a plant or animal. In biology, it may contain or protect fluid, eggs, spores, reproductive material, or organs, as in an egg sac or a seminal sac. The word can also refer more generally to a small bag or pouch, though “pouch” and “bag” are often more natural in everyday speech. “Sac” is especially useful when describing something that is anatomically or botanically pouch-shaped rather than simply container-like. Its precise, slightly formal tone makes it common in scientific writing but less frequent in casual conversation. Many familiar natural objects are described as sacs, including the fluid-filled sacs of certain plants and the protective egg sacs made by spiders and other animals.
nounA pouchlike structure, especially one in a plant or animal that contains or encloses a fluid, organ, or reproductive material. More generally, it can mean a bag or container.
- A pouchlike structure in a plant or animal, often containing or enclosing fluid, reproductive material, eggs, or other contents.
- A small bag or pouch, especially one made from cloth or another flexible material.
- Any saclike anatomical or botanical structure.
"The female spider carefully guarded her egg sac until the young spiders were ready to emerge."
"The insect stores nutrients in a small sac near its mouth."
"She tied the herbs into a small cloth sac before placing it in the cupboard."
The plural is regular and adds “-s”; in biological contexts, “sacs” may refer to multiple pouchlike structures or organs.
"The frog has paired vocal sacs that amplify its calls."
A spider’s egg sac is one of nature’s tiny nursery rooms, protecting dozens of developing young while they wait to hatch.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does sac come from?
The word comes through Middle English from Old French sac, a borrowing of Latin saccus, meaning “bag” or “sack.” In Latin, the word was used for containers and developed into the modern biological sense through the comparison of saclike structures in living organisms. The English word sack is a cognate with the same Latin origin, while forms such as saccate and sacciform preserve the Latin root in botanical and anatomical descriptions.
Related word forms
How sac is actually used
In biology and botany, the word is technical but widely understandable. In general usage, it is less common than “pouch” or “bag” and may sound formal or literary.
Easily confused with sac
A sac is usually a biological pouch or a small bag-like structure, while a sack is generally a larger flexible container made from cloth or paper.