The Collaborative International Dictionary of English v.0.48:

Subdued \Sub*dued"\, a.
   1. Conquered; overpowered; crushed; submissive; mild.
      [1913 Webster]

   2. Not glaring in color; soft in tone.
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The Collaborative International Dictionary of English v.0.48:

Subdue \Sub*due"\, v. t. [imp. & p. p. Subdued; p. pr. & vb.
   n. Subduing.] [OE. soduen, OF. sosduire to seduce, L.
   subtus below (fr. sub under) + ducere to lead. See Duke,
   and cf. Subduct.]
   1. To bring under; to conquer by force or the exertion of
      superior power, and bring into permanent subjection; to
      reduce under dominion; to vanquish.
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            I will subdue all thine enemies.      --1 Chron.
                                                  xvii. 10.
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   2. To overpower so as to disable from further resistance; to
      crush.
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            Nothing could have subdued nature
            To such a lowness, but his unkind daughters. --Shak.
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            If aught . . . were worthy to subdue
            The soul of man.                      --Milton.
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   3. To destroy the force of; to overcome; as, medicines subdue
      a fever.
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   4. To render submissive; to bring under command; to reduce to
      mildness or obedience; to tame; as, to subdue a stubborn
      child; to subdue the temper or passions.
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   5. To overcome, as by persuasion or other mild means; as, to
      subdue opposition by argument or entreaties.
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   6. To reduce to tenderness; to melt; to soften; as, to subdue
      ferocity by tears.
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   7. To make mellow; to break, as land; also, to destroy, as
      weeds.
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   8. To reduce the intensity or degree of; to tone down; to
      soften; as, to subdue the brilliancy of colors.
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   Syn: To conquer; overpower; overcome; surmount; vanquish. See
        Conquer.
        [1913 Webster]

WordNet (r) 3.0 (2006):

subdued
    adj 1: in a softened tone; "hushed voices"; "muted trumpets"; "a
           subdued whisper"; "a quiet reprimand" [syn: hushed,
           muted, subdued, quiet]
    2: restrained in style or quality; "a little masterpiece of low-
       keyed eloquence" [syn: low-key, low-keyed, subdued]
    3: quieted and brought under control; "children were subdued and
       silent"
    4: not brilliant or glaring; "the moon cast soft shadows"; "soft
       pastel colors"; "subdued lighting" [syn: soft, subdued]
    5: lacking in light; not bright or harsh; "a dim light beside
       the bed"; "subdued lights and soft music" [syn: dim,
       subdued]