Source : Webster's Revised Unabridged Dictionary (1913)

Plexus \Plex"us\, n.; pl. L. {Plexus}, E. {Plexuses}. [L., a
   twining, braid, fr. plectere, plexum, to twine, braid.]
   1. (Anat.) A network of vessels, nerves, or fibers.

   2. (Math.) The system of equations required for the complete
      expression of the relations which exist between a set of
      quantities. --Brande & C.