Archaic KJV Word
Love
Modern equivalent: love (no real alternative exists)
What Was Lost
The entire taxonomy of love. When John wrote 'God is agape,' he meant God is self-giving, sacrificial, covenant-keeping love -- not that God is a warm feeling. When the same English word describes God's sacrifice on the cross and a preference for pizza, the theological vocabulary has collapsed.
Closest Survivor in Modern English
agape (increasingly used untranslated in theological contexts because English 'love' is too broad)
Peak Usage (1611)
KJV John 3:16 -- 'God so loved the world'; 1 John 4:8 -- 'God is love'
Died still used but catastrophically diluted (~1800)
English has one word where Greek had four (agape, phileo, storge, eros) and Hebrew had multiple (ahavah, chesed, rachamim). 'Love' collapsed an entire theological vocabulary into a single overloaded word.
What Replaced It
“love”
The replacement IS the problem -- one word now covers romantic desire, divine sacrifice, friendship affection, and family bonds indiscriminately
“care about”
Shallow and noncommittal; agape love was covenantal self-sacrifice