An Etymological Dictionary of Astronomy and Astrophysics

1. A devastating flood; deluge.
   

2. Any violent upheaval that brings about great changes or causes great demolition. See also: → catastrophe.

Etymology (EN): From Fr. cataclysme, from L. cataclysmos “deluge,” from Gk. kataklysmos, from kataklyzein “to inundate,” from kata “down” + klyzein “to wash.”

Etymology (PE): Gatlur “great flood,” from gat “great, large, big” [Mo’in, Dehxodâ] + lur “flood” [Mo’in, Dehxodâ], cf. Gk. louein “to wash,” L. luere “to wash,”
Bret. laouer “trough,” PIE *lou- “to wash.” Variants of lur in Pers. dialects are: Lori, Kordi laf, lafow, lafaw, Tabari lé,
all meaning “flood.”