bacterium [M19th] This modern Latin term is formed from Greek baktērion ‘little staff’; the first bacteria to be discovered were rod-shaped. The word bacillus [L19th], a pathogenic bacterium, also meant ‘little rod’ in late Latin. Bacillus is also behind the French word debacle, adopted into English in the early 19th century. It literally means an unbarring and was first used of the breaking of ice or other blockage in a river and its effects, and then transferred to human behaviour.