Source : Webster's Revised Unabridged Dictionary (1913)

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. (Zo["o]l.) 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.

Commensal \Com*men"sal\, a.
   Having the character of a commensal.

Source : WordNet®

commensal
     n : either of two different animal or plant species living in
         close association but not interdependent

commensal
     adj : living in a state of commensalism