'atypic' originates from Greek, specifically the word 'atypikos', where 'a-' meant 'not' and 'typikos' meant 'of a type or form.'

'atypikos' passed into New Latin as 'atypicus' and later entered English as 'atypic' (used from the 19th century, especially in medical contexts).

Initially it meant 'not of a type' (literally 'without type'), but over time it evolved into the current meaning of 'not typical; irregular or abnormal'.