Archaic KJV Word
Lewd
Modern equivalent: vulgar
What Was Lost
The class dimension of moral language. The 'lewd fellows of the baser sort' in Acts were not sexual deviants but uneducated, common ruffians -- mob elements. The word described social station and willful ignorance, not sexual behavior. Its narrowing to only sexual meaning erased the biblical concern with willful ignorance as a moral failing.
Closest Survivor in Modern English
laity (from the same root, meaning non-clergy/common people)
Peak Usage (1611)
KJV Acts 17:5 -- 'Certain lewd fellows of the baser sort'
Died ~1750
Shifted from 'unlearned/lay/common/ignorant' (from Old English laewede 'non-clerical') to exclusively 'sexually obscene,' sexualizing what was originally a class and education distinction.
What Replaced It
“ignorant”
Neutral and correctable; lewd implied willful low-mindedness, choosing to remain common
“vulgar”
Closest match -- also originally meant 'common/of the people' before becoming sexual
“unlearned”
Simply lacking education; lewd suggested the person's commonness was a moral condition