Archaic KJV Word
Veil
Modern equivalent: curtain
What Was Lost
The dimensional boundary. The veil was not a curtain but a cosmic membrane between God's dimension and ours. It simultaneously protected humans from being destroyed by God's direct presence and symbolized the separation sin had caused. When it tore at the crucifixion, the boundary between heaven and earth was ripped open -- access to God's presence was thrown wide.
Closest Survivor in Modern English
veil (still used in Christian theology with rich meaning, but broader culture has lost the cosmic dimension)
Peak Usage (1611)
KJV Exodus 26:33 -- 'The veil shall divide unto you between the holy place and the most holy'; Hebrews 10:20 -- 'Through the veil, that is to say, his flesh'
Died still used but fashion-ized (~1800)
Hebrew paroket ('the thick curtain separating humanity from God's direct presence/the barrier between life and death') was reduced to wedding fashion and face covering. The cosmic boundary between dimensions became fabric.
What Replaced It
“curtain”
Interior decoration; the veil was the boundary between the human world and God's unmediated presence
“barrier”
Generic obstacle; the veil was specifically what prevented humans from dying in God's presence
“covering”
Physical concealment; the veil was a theological boundary between dimensions of reality