Archaic KJV Word
Know
Modern equivalent: understand
What Was Lost
The intimacy. Yada was used for the most intimate human act ('Adam knew Eve'), for God's knowledge of people ('Before I formed thee, I knew thee'), and for the goal of human existence ('that they might know thee'). Knowing God was not studying theology but entering an intimate, transformative relationship. Eternal life was not information but intimacy.
Closest Survivor in Modern English
know (still used in the intimacy sense in legal language -- 'carnal knowledge' -- but otherwise purely cognitive)
Peak Usage (1611)
KJV Genesis 4:1 -- 'Adam knew Eve his wife'; John 17:3 -- 'This is life eternal, that they might know thee'
Died still used but intellectualized (~1700)
Hebrew yada ('to know intimately/experience/encounter/be in relationship with') reduced to 'possess information about.' The most intimate word in Hebrew became a cognitive function.
What Replaced It
“understand”
Intellectual comprehension; yada included physical, emotional, and relational dimensions
“be aware of”
Surface-level; yada was the deepest possible encounter between persons
“have information about”
Data possession; yada was experienced intimacy, not accumulated facts