'slovenly' originates from English, specifically formed from the noun 'sloven' plus the adjectival suffix '-ly', where 'sloven' meant 'a careless or untidy person'.

'sloven' existed in Middle English (forms such as 'sloven'), and by suffixation with '-ly' in early modern English the adjective 'slovenly' developed to describe the qualities of a 'sloven'.

Initially it referred to someone who was a 'sloven' (an untidy person); over time it came to describe characteristics or actions that are 'untidy' or 'careless' and also the adverbial manner 'in a slovenly way'.