Definition of "commensal" [com•men•sal]

• Of, relating to, or characterized by a symbiotic relationship in which one species is benefited while the other is unaffected. (adjective)
• An organism participating in a symbiotic relationship in which one species derives some benefit while the other is unaffected. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "These beneficial bugs are called commensal bacteria."
• "He who lives at the expense of another, and at his table, is his "commensal"."
• "Over millions of years, it has learned to live benignly on human skin and in human nostrils, in a microscopic intimacy that biologists call “commensal,” from the Latin words for “being at table together.”"