Synonyms for Sac (same or very similar meaning)
WordNet sense 1 (an enclosed space):
pocket, pouch, sackWordNet sense 2 (a case or sheath especially a pollen sac or moss capsule):
thecaWordNet sense 3 (a member of the Algonquian people formerly living in Wisconsin in the Fox River valley and on the shores of Green Bay):
SaukFrom the ODE community, based on WordNetadd/edit