'bacillicidal' originates from Latin (via Neo-Latin), specifically the word 'bacillus' and the Latin combining element '-cidus'/'-cidal', where 'bacillus' meant 'little staff/rod' (diminutive of 'baculum') and '-cidus' (from 'caedere') meant 'to kill'.

'bacillicidal' is a modern English scientific formation from Neo-Latin components: 'bacillus' (rod-shaped bacterium) + suffix '-cidal' (from Latin forming adjectives meaning 'killing'), producing the adjective meaning 'killing bacilli'; variant spellings such as 'bacillocidal' have also appeared in technical usage.

Initially, formation denoted 'capable of killing bacilli' and this specific meaning has been retained in modern scientific and technical usage.