From Merriam-Websters online dictionary:
Pronunciation: (?)kas-?k?d
Function: noun
Etymology: French, from Italian cascata, from cascare to fall, from Vulgar Latin *casicare, from Latin casus fall
Date: 1641
1 : a steep usually small fall of water; especially : one of a series
2 a : something arranged or occurring in a series or in a succession of stages so that each stage derives from or acts upon the product of the preceding <blood clotting involves a biochemical cascade> b : a fall of material (as lace) that hangs in a zigzag line
3 : something falling or rushing forth in quantity <a cascade of sound> <a cascade of events>
Main Entry: 2cascade
Function: verb
Inflected Form(s): cas·cad·ed; cas·cad·ing
Date: 1702
intransitive verb : to fall, pour, or rush in or as if in a cascadetransitive verb 1 : to cause to fall like a cascade
2 : to connect in a cascade arrangement
Because the rules set in the stylesheet cascade down through the elements.