n. pl. ba·cil·li (-sĭlī′)
1. Any of various bacteria, especially a rod-shaped bacterium.
2. Any of various rod-shaped, spore-forming, aerobic bacteria of the genus Bacillus that often occur in chains and include B. anthracis, the causative agent of anthrax.
[Late Latin, diminutive of Latin baculum, rod; see bak- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.