cisterna (pl. cisternae) Any of the membrane-bound sacs that form the branches of the endoplasmic reticulum (ER) and Golgi apparatus. The cisternae of the ER are continuous with each other and with the nuclear envelope; in rough ER the cisternae are flattened sacs, whereas in smooth ER they are more tubular in shape.

cisterna (sis-ter-nă) n. (pl. cisternae)
1. one of the enlarged spaces beneath the arachnoid that act as reservoirs for cerebrospinal fluid. c. magna the largest of the cisternae, lying beneath the cerebellum and behind the medulla oblongata.

2. a dilatation at the lower end of the thoracic duct, into which the great lymph ducts of the lower limbs drain.