bacillus
Pronunciation: /bəˈsɪləs/
noun ( plural bacilli /-lʌɪ, -liː/)

Origin:
late 19th century: from late Latin, diminutive of Latin baculus 'stick'

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.