Archaic KJV Word
Light
Modern equivalent: brightness
What Was Lost
The inseparability of physical and spiritual light. In Hebrew thought, light was not a metaphor for truth -- light WAS truth made visible. God's first creative word produced light because God Himself is light. 'I am the light of the world' was not a metaphor but a claim of identity with the first thing God ever made.
Closest Survivor in Modern English
light (still used metaphorically but the theological-physical unity has been severed)
Peak Usage (1611)
KJV Genesis 1:3 -- 'Let there be light'; John 8:12 -- 'I am the light of the world'
Died still used but physicalized (~1700)
Hebrew or ('light') carried theological weight as God's first creative act and a metaphor for His presence, truth, and salvation. Scientific revolution reduced 'light' to electromagnetic radiation, severing the physical from the theological.
What Replaced It
“illumination”
Physical phenomenon; or was the first manifestation of divine order over chaos
“photons”
Scientific particles; biblical light was the visible expression of God's presence in the world
“enlightenment”
Intellectual awakening; or was God's own radiance entering creation