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]

The Collaborative International Dictionary of English v.0.48:

Descend \De*scend"\, v. i. [imp. & p. p. Descended; p. pr. &
   vb. n. Descending.] [F. descendre, L. descendere,
   descensum; de- + scandere to climb. See Scan.]
   1. To pass from a higher to a lower place; to move downwards;
      to come or go down in any way, as by falling, flowing,
      walking, etc.; to plunge; to fall; to incline downward; --
      the opposite of ascend.
      [1913 Webster]

            The rain descended, and the floods came. --Matt.
                                                  vii. 25.
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            We will here descend to matters of later date.
                                                  --Fuller.
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   2. To enter mentally; to retire. [Poetic]
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            [He] with holiest meditations fed,
            Into himself descended.               --Milton.
      [1913 Webster]

   3. To make an attack, or incursion, as if from a vantage
      ground; to come suddenly and with violence; -- with on or
      upon.
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            And on the suitors let thy wrath descend. --Pope.
      [1913 Webster]

   4. To come down to a lower, less fortunate, humbler, less
      virtuous, or worse, state or station; to lower or abase
      one's self; as, he descended from his high estate.
      [1913 Webster]

   5. To pass from the more general or important to the
      particular or less important matters to be considered.
      [1913 Webster]

   6. To come down, as from a source, original, or stock; to be
      derived; to proceed by generation or by transmission; to
      fall or pass by inheritance; as, the beggar may descend
      from a prince; a crown descends to the heir.
      [1913 Webster]

   7. (Anat.) To move toward the south, or to the southward.
      [1913 Webster]

   8. (Mus.) To fall in pitch; to pass from a higher to a lower
      tone.
      [1913 Webster]

WordNet (r) 3.0 (2006):

descending
    adj 1: coming down or downward [ant: ascending(a)]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "descending":
   ascending, axial, back, back-flowing, backward, collapsing,
   deciduous, declined, declining, declivate, declivitous, declivous,
   decurrent, descendant, dipping, down, down-reaching, down-trending,
   downcoming, downfalling, downgoing, downgrade, downhill,
   downsinking, downward, drifting, drooping, dropping, falling,
   flowing, fluent, flying, going, gyrational, gyratory, mounting,
   on the descendant, on the downgrade, passing, plummeting, plunging,
   progressive, reflowing, refluent, regressive, retrogressive,
   rising, rotary, rotational, rotatory, running, rushing, sagging,
   setting, sideward, sinking, soaring, streaming, submerging,
   subsiding, tottering, tumbledown, up-trending, upward