cataclysm (n.)

"a deluge, a flood," originally especially "Noah's flood," 1630s, from French cataclysme (16c.), from Latin cataclysmos or directly from Greek kataklysmos "deluge, flood, inundation," from kataklyzein "to deluge," from kata "down" (see cata-) + klyzein "to wash," from PIE *kleue- "to wash, clean" (see cloaca).