Sac

(noun) an enclosed space. Synonyms: pouch, sac, sack, pocket. Example: "The trapped miners found a pocket of air."

(noun) a case or sheath especially a pollen sac or moss capsule. Synonyms: theca, sac.

(noun) a member of the Algonquian people formerly living in Wisconsin in the Fox River valley and on the shores of Green Bay. Synonyms: Sauk.

(noun) a structure resembling a bag in an animal. Synonyms: sac.