the.com/sac

means A pouch-like structure in a plant or animal that holds a liquid, gas, or other substance — anatomy's catch-all bag.

from From French 'sac,' from Latin 'saccus' meaning a bag or sack, which itself goes back to Greek 'sakkos' — a word for coarse cloth or sacking, possibly borrowed from a Semitic language (compare Hebrew 'saq'). So the venom sac in a snake's mouth shares its deepest root with the burlap sack you'd haul potatoes in — both are, etymologically, just containers.