Archaic KJV Word
Jubilee
Modern equivalent: big anniversary party
What Was Lost
The economic revolution. Every fifty years: all debts cancelled, all slaves freed, all ancestral land returned to the original families. Jubilee was God's economic immune system -- preventing permanent poverty, permanent debt slavery, and permanent wealth concentration. When Jesus announced 'the year of the Lord's favor' in Luke 4, He was declaring jubilee.
Closest Survivor in Modern English
jubilee (still used for celebrations but the radical economic-justice content is entirely forgotten)
Peak Usage (1611)
KJV Leviticus 25:10 -- 'Ye shall hallow the fiftieth year, and proclaim liberty throughout all the land'
Died still used but party-ified (~1900)
Hebrew yovel ('ram's horn blast/the great liberation/the year all debts were cancelled, all slaves freed, and all land returned to original families') reduced to 'big anniversary celebration.' The revolutionary economic justice was lost to party planning.
What Replaced It
“anniversary”
Calendar milestone; jubilee was an economic revolution -- total debt cancellation and wealth redistribution
“celebration”
Festive event; jubilee was the most radical economic legislation in ancient history
“milestone”
Achievement marker; jubilee was God's built-in economic reset preventing permanent poverty and permanent wealth