The Collaborative International Dictionary of English v.0.48:

Node \Node\ (n[=o]d), n. [L. nodus; perh. akin to E. knot. Cf.
   Noose, Nowed.]
   1. A knot, a knob; a protuberance; a swelling.
      [1913 Webster]

   2. Specifically:
      (a) (Astron.) One of the two points where the orbit of a
          planet, or comet, intersects the ecliptic, or the
          orbit of a satellite intersects the plane of the orbit
          of its primary.
      (b) (Bot.) The joint of a stem, or the part where a leaf
          or several leaves are inserted.
      (c) (Dialing) A hole in the gnomon of a dial, through
          which passes the ray of light which marks the hour of
          the day, the parallels of the sun's declination, his
          place in the ecliptic, etc.
      (d) (Geom.) The point at which a curve crosses itself,
          being a double point of the curve. See Crunode, and
          Acnode.
      (e) (Mech.) The point at which the lines of a funicular
          machine meet from different angular directions; --
          called also knot. --W. R. Johnson.
      (f) (Poet.) The knot, intrigue, or plot of a piece.
      (g) (Med.) A hard concretion or incrustation which forms
          upon bones attacked with rheumatism, gout, or
          syphilis; sometimes also, a swelling in the
          neighborhood of a joint. --Dunglison.
      (h) (Mus) One of the fixed points of a sonorous string,
          when it vibrates by aliquot parts, and produces the
          harmonic tones; nodal line or point.
      (i) (Zool.) A swelling.
          [1913 Webster]

   3. (Math., Computers) A special point in a graph or diagram
      which is attached to other points by links. It is often
      labeled and represented graphically as a box or circle. A
      node may represent any object which is related to other
      objects in a conceptual structure that can be represented
      as a graph, the relations being represented as links
      between the nodes.
      [PJC]

   4. (Anat.) A small mass of tissue differing from other tissue
      in its immediate vicinity; as, a lymph node.
      [PJC]

   Ascending node (Astron.), the node at which the body is
      passing northerly, marked with the symbol [astascending],
      called the Dragon's head. Called also northern node.

   Descending node, the node at which the body is moving
      southwardly, marked thus [astdescending], called Dragon's
      tail.

   Line of nodes, a straight line joining the two nodes of an
      orbit.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Descending \De*scend"ing\, a.
   Of or pertaining to descent; moving downwards.
   [1913 Webster]

   Descending constellations or Descending signs (Astron.),
      those through which the planets descent toward the south.


   Descending node (Astron.), that point in a planet's orbit
      where it intersects the ecliptic in passing southward.

   Descending series (Math.), a series in which each term is
      numerically smaller than the preceding one; also, a series
      arranged according to descending powers of a quantity.
      [1913 Webster]

WordNet (r) 3.0 (2006):

descending node
    n 1: the point at which an orbit crosses the ecliptic plane
         going south [ant: ascending node]