'criminal' originates from Late Latin, specifically the word 'criminalis', where 'crimen' meant 'charge, accusation'.

'criminal' changed from Old French 'criminel' and Middle English forms derived from Latin 'criminalis' and eventually became the modern English word 'criminal' (and the adverbial form 'criminally').

Initially it meant 'relating to a charge or accusation (of crime)', but over time it retained that sense and also extended metaphorically to mean 'shamefully or blameworthily' (as in 'criminally underrated').