Definition of bacillus in English:



  • 1A rod-shaped bacterium.

    • ‘The victim carried an enormous number of bacilli shaped with the typical ‘short rounded ends.’’
    • ‘One is a microscopic rod-shaped bacterium called bacillus anthracis, easy to grow in the lab but fragile and easily killed in the open.’
    • ‘At far right, Methanobacterium thermoautotrophicum, an elongate bacillus form.’
    1. 1.1 A disease-causing bacterium.
      ‘the bacillus was thought to have proliferated in water polluted by sewage’
      ‘tubercle bacilli’
      • ‘When infectious people cough, sneeze, talk or spit, they propel TB germs, known as bacilli, into the air.’
      • ‘The isolation of the tuberculosis bacillus in 1882 by Robert Koch, who later became professor of hygiene and director of the Institute for Infectious Diseases in Berlin, was a scientific breakthrough.’
      • ‘The book ends with the haunting observation that although the plague bacillus can go into hiding for years and years, it never dies or disappears for good.’
      • ‘The man, who is unidentified as yet, does not have anthrax - the bacillus is on his person, but he's not infected, and with proper treatment, he should be fine.’
      • ‘Currently a third of the world's population carry the bacillus, albeit in a dormant form.’
      illness, ailment, infection, disease, disorder, sickness, affliction, malady, complaint, upset, condition, infirmity, indisposition, malaise
      View synonyms


All bacteria belonging to the genus Bacillus are called bacilli. However, there are some bacteria, also called bacilli, which do not belong to the genus Bacillus


Late 19th century: from late Latin, diminutive of Latin baculus ‘stick’.