The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. (Math.) The system of equations required for the complete
      expression of the relations which exist between a set of
      quantities. --Brande & C.
      [1913 Webster]

   3. A network; an intricate or interwoven combination of
      elements or parts in a coherent structure.

            In the perception of a tree the reference to an
            object is circumscribed and directed by a plexus of
            visual and other presentations.       --G. F. Stout.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

plexus
    n 1: a network of intersecting blood vessels or intersecting
         nerves or intersecting lymph vessels [syn: plexus,
         rete]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "plexus":
   afferent neuron, arabesque, autonomic nervous system, axon,
   basketry, basketwork, brain, cancellation, central nervous system,
   cerebral cortex, craniosacral nervous system, cross-hatching,
   crossing-out, dendrite, effector organ, efferent neuron, filigree,
   fret, fretwork, ganglion, grate, grating, gray matter, grid,
   gridiron, grille, grillwork, hachure, hatching, interlacement,
   internuncial neuron, intertexture, intertwinement, lace, lacery,
   lacework, lacing, lattice, latticework, medullary sheath, mesh,
   meshes, meshwork, nerve, nerve trunk, nervous system, net, netting,
   network, neuron, peripheral nervous system, plexure, raddle,
   reticle, reticulation, reticule, reticulum, riddle, screen,
   screening, sensorium, sensory area, sensory cell, sieve,
   solar plexus, spinal cord, synapse, texture,
   thoracolumbar nervous system, tissue, tracery, trellis,
   trelliswork, wattle, weave, weaving, web, webbing, webwork, weft,
   white matter, wicker, wickerwork



The Free On-line Dictionary of Computing (30 December 2018):

Plexus

   A modular web server written in Perl by Tony
   Sanders .  Comes with interfaces to allow
   many other information services to be served via the Web.

   Version 3.0m 1994-07-22 (ftp://ftp.earth.com/plexus/).

   (1994-07-22)