n. pl. rhi·zo·bi·a (-bē-ə)
Any of various aerobic bacteria of the genus Rhizobium that form root nodules in leguminous plants, such as clover and beans, where they establish a symbiotic relationship in which the bacteria obtain carbon and energy from the plant while supplying the plant with nitrogen by nitrogen fixation.
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.