Meaning

noun a sac or cavity containing fluid especially lymph or cerebrospinal fluid

noun a tank that holds the water used to flush a toilet

noun an artificial reservoir for storing liquids; especially an underground tank for storing rainwater

originFrom Middle English cisterne, from Old French cisterne (Modern French citerne) from Latin cisterna, from cista (“box”), from Ancient Greek κίστη (kístē, “box”). Doublet of cisterna.

Etymology from Wiktionary, CC BY-SA 3.0