'witless' originates from Old English, specifically from the elements 'wit' and the suffix '-less', where 'wit' meant 'mind, understanding' and '-less' meant 'without'.

'witless' descended from Old English 'witleas' (also spelled 'wítlēas'), passed into Middle English as 'witless', and eventually became the modern English 'witless'.

Initially, it meant 'without knowledge or understanding', and over time it has retained a similar meaning of 'lacking sense or intelligence' though it is now often used in informal or emphatic contexts.