Why is it called "doomsday"? Neither the wiki article nor MW dictionary definition explain this etnymology/usage.
-- https://www.rudy.ca/doomsday.html
Likely that sprung to mind because of the "Domesday Book":
"Domesday Book (/ˈduːmzdeɪ/ DOOMZ-day; the Middle English spelling of "Doomsday Book") is a manuscript record of the Great Survey of much of England and parts of Wales completed in 1086 at the behest of King William the Conqueror."