com·men·sal /kəˈmɛn(t)səl/
  (a.)共餐的,同吃的,共生的共食伴,共生物
  com·men·sal /kəˈmɛn(t)səl/ 形容詞
  共生的,共棲的,共生體,共棲體
  Com·men·sal n.
  1. One who eats at the same table. [Obs.]
  2. Zool. 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.
  Com·men·sal a. Having the character of a commensal.
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  commensal
       adj : living in a state of commensalism
       n : either of two different animal or plant species living in
           close association but not interdependent