1. Relating to or descriptive of those who habitually eat together: "Carlos and his family made every effort to eat their evening meals together, even when there were activities that could interfere with their commensal meals; such as, television programs or evening sports events."
2. Living in a relationship when one organism gets food or other benefits from another organism or group without doing any harm to it: "The intestines have competition between the naturally commensal bacteria that live in the intestinal tract and any invading bacteria."
3. Etymology: from the Latin prefix com- meaning "with, together, jointly" and the Latin adjective mensalis, meaning "of the table."

In its earliest English uses, commensal referred to people who ate together, but about 1870, biologists started using it for organisms and since then, the scientific sense has almost completely replaced the "dining" idea.