Archaic KJV Word
Repentance
Modern equivalent: feeling guilty
What Was Lost
The new mind. Meta (change) + nous (mind) = a completely new way of thinking. Repentance was not primarily feeling bad but receiving a new mind -- seeing God, yourself, and the world with completely different eyes. 'Repentance unto life' was not 'guilt leading to sadness' but 'a transformed mind leading to new life.'
Closest Survivor in Modern English
repentance (still used but dominated by guilt rather than transformation)
Peak Usage (1611)
KJV Luke 15:7 -- 'Joy shall be in heaven over one sinner that repenteth'; Acts 11:18 -- 'God also to the Gentiles granted repentance unto life'
Died still used but guilt-ified (~1800)
Greek metanoia ('complete change of mind/total reorientation of thinking/fundamental paradigm shift') guilt-ified into 'feeling bad about what you did.' The forward-looking transformation became backward-looking regret.
What Replaced It
“remorse”
Backward-looking guilt; metanoia was forward-looking transformation
“penance”
Punishment for wrongdoing; metanoia was a gift that reoriented your entire life
“contrition”
Sorrow for sin; metanoia was a new mind -- seeing everything differently