'bacillosis' originates from Neo-Latin/modern Latin, specifically from 'bacillus' (a diminutive of Latin 'bacillum', itself from 'baculum' meaning 'stick' or 'rod') combined with the Greek-derived suffix '-osis' meaning 'disease or abnormal condition'.

'bacillus' derives from Latin 'bacillum' (a diminutive of 'baculum' 'stick/rod'), and the suffix '-osis' comes from Greek 'osis' meaning a state or disease; the compound 'bacillosis' was formed in modern medical Latin (late 19th century) to denote diseases caused by bacilli.

Initially, it meant 'a condition involving bacilli'; over time it has remained focused on 'infection or disease caused by bacilli' in medical usage.