Commensal
(Com*men"sal) n. [LL. commensalis; L. com- + mensa table: cf. F. commensal. Cf. Mensal.]

1. One who eats at the same table. [Obs.]

2. (Zoöl.) An animal, not truly parasitic, which lives in, with, or on, another, partaking usually of the same food. Both species may be benefited by the association.

Believe it or not, I recently on Internet read that some
patients are more comfortable with a chosen intestinal parasite than without any.