Sac (noun)

1. A bag or container, typically made of a flexible material such as cloth, paper, or plastic, that can be closed with a drawstring or zipper.
2. A bag or pouch, especially one that is filled with fluid or gas.

Origin:

Late middle english: from old french, from latin saccus "bag, sack".

Examples:

1. He placed the money in a sac.
2. The sac of fluid was removed during the surgery.
3. The sac containing the air was punctured.
4. The sac was filled with helium.
5. The sac was filled with water and used as a flotation device.