Archaic KJV Word
Revelation
Modern equivalent: end-times catastrophe
What Was Lost
The unveiling. Apokalypsis simply meant pulling the cover off something -- like removing a sheet from a statue. The Revelation of Jesus Christ was not primarily about future destruction but about the unveiling of who Jesus really is. Every revelation was God lifting the curtain so humans could see reality as it actually is.
Closest Survivor in Modern English
revelation (still used in Christian theology with strong meaning; broader culture equates it with catastrophe)
Peak Usage (1611)
KJV Revelation 1:1 -- 'The Revelation of Jesus Christ, which God gave unto him'; Galatians 1:12 -- 'I received it by the revelation of Jesus Christ'
Died still used but sensationalized (~1900)
Greek apokalypsis ('unveiling/uncovering/pulling back the curtain to show what was always there') sensationalized into 'apocalyptic destruction' or restricted to the last book of the Bible.
What Replaced It
“apocalypse”
Destruction and catastrophe; apokalypsis was simply an unveiling -- showing what was hidden
“end times”
Futuristic and fearful; revelation was God pulling back the curtain on present reality
“insight”
Human discovery; revelation was God actively choosing to show what could not otherwise be seen