Archaic KJV Word
Mansion
Modern equivalent: dwelling places
What Was Lost
The intimacy of dwelling with God. Jesus promised not gold-plated palaces but permanent dwelling places in His Father's house -- rooms where the Father's children would live, remain, abide. The word was about permanence and belonging, not luxury and size. 'Many mansions' meant 'room for everyone to stay' -- abundance of welcome, not square footage.
Closest Survivor in Modern English
manse (a clergy residence -- a dwelling place, not a luxury estate)
Peak Usage (1611)
KJV John 14:2 -- 'In my Father's house are many mansions'
Died ~1800
Inflated from 'dwelling place/room/abiding place' (Latin mansio 'a staying/dwelling' from manere 'to remain') to 'a very large, luxurious house,' turning Jesus's promise of intimate dwelling with the Father into a real estate prospectus.
What Replaced It
“rooms”
Generic and small; mansion-as-dwelling-place meant a permanent abode prepared specifically for you
“dwelling places”
Closer but compound; mansion was a single word for 'a place where you will remain'
“homes”
Domestic; mansion carried the permanence of being settled forever