Archaic KJV Word
Heart
Modern equivalent: emotions/feelings
What Was Lost
The integrated command center. In Hebrew, the heart was where you thought, planned, decided, and felt -- all together. There was no head-vs-heart split. 'Keep thy heart' meant guard the core from which every decision, thought, feeling, and action originates. It was not sentimental advice but strategic command.
Closest Survivor in Modern English
heart (still used but almost exclusively means emotions, losing the thinking/willing dimensions)
Peak Usage (1611)
KJV Proverbs 4:23 -- 'Keep thy heart with all diligence; for out of it are the issues of life'
Died still used but sentimentalized (~1800)
Hebrew lev/levav ('the center of thought, will, and decision-making') was reduced to the seat of emotions only, thanks to Enlightenment separation of reason and feeling. The heart lost its mind.
What Replaced It
“emotions”
Only one function; the Hebrew heart thought, decided, planned, and felt
“feelings”
Passive and subjective; lev was the active command center of the whole person
“mind”
Purely cognitive; lev included will, intention, and desire alongside thought