'atrabiliary' originates from Latin, specifically the Late Latin/Medieval Latin word 'atrābilis' (or 'atrabiliosus'), where 'ater' meant 'black' and 'bilis' meant 'bile'.

'atrābilis' passed into Medieval/Late Latin as 'atrabiliosus', entered Middle English as 'atrabilious', and in English the form 'atrabiliary' developed as an adjective form related to 'atrabilious'.

Initially it referred to the concept of 'black bile' or being 'affected by black bile' (a humoral theory cause of melancholy); over time it came to describe a person's temperament as 'melancholic' or 'bilious/ill-tempered'.