From Old English 'lǣwede' (layperson, non-clergy), degrading over centuries through 'ignorant' to 'vulgar' to 'sexually obscene.'
Crude and offensive in a sexual way; obscene.
From Old English 'lǣwede' meaning 'non-clerical, of the laity' — an ordinary person who wasn't part of the clergy. Since laypeople were considered uneducated and vulgar compared to monks and priests, 'lewd' shifted from 'non-clergy' to 'ignorant' to 'vulgar' to 'sexually obscene.' Key roots: lǣwede (Old English: "layperson, non-clergy").
'Lewd' originally just meant 'not a priest.' Old English 'lǣwede' described any layperson. But medieval clergy considered themselves the educated class and laypeople as ignorant, so 'lewd' shifted to 'uneducated.' Then 'uneducated' became 'vulgar,' and 'vulgar' became 'sexually obscene.' The word's journey — from 'normal person' to 'sexual deviant' — perfectly maps the medieval Church's dim view of everyone who wasn't a monk.