'non-lettered' originates from Latin and Latin via Old French and Middle English, specifically the words 'non' and 'littera', where 'non' meant 'not' and 'littera' meant 'letter; learning'.

'lettered' came through Old French 'lettre' from Latin 'littera' into Middle English as 'lettered' (meaning 'learned'), and the privative prefix 'non-' was added in Modern English, forming the current compound 'non-lettered'.

Initially, 'lettered' meant 'learned; educated in letters'; with the addition of 'non-', the sense became 'not learned/illiterate', and it is also used literally for things 'without letters'.