Archaic KJV Word
Froward
Modern equivalent: perverse
What Was Lost
The directional moral language. Froward was the antonym of toward -- one was facing-toward-God, the other facing-away-from-God. English lost this spatial moral vocabulary. A froward heart was literally a heart turned in the wrong direction. You could not be accidentally froward; it required deliberate rotation away from the good.
Closest Survivor in Modern English
perverse (in its older sense of 'turned the wrong way')
Peak Usage (1611)
KJV Proverbs 4:24 -- 'Put away from thee a froward mouth'; Psalm 101:4 -- 'A froward heart shall depart from me'
Died ~1800
The word simply died, leaving no direct replacement. 'Froward' (opposite of 'toward' -- turned away from, perverse) had no successor that captured its specific meaning of willful perversity.
What Replaced It
“perverse”
Sexual connotations in modern usage; froward meant morally twisted/turned away from the good without sexual implication
“stubborn”
Passive resistance; froward was active -- deliberately turning away, choosing the opposite of what is right
“crooked”
Physical metaphor; froward was moral and directional -- facing away from God