The Collaborative International Dictionary of English v.0.48:

Soft \Soft\ (s[o^]ft; 115), a. [Compar. Softer
   (s[o^]ft"[~e]r); superl. Softest.] [OE. softe, AS.
   s[=o]fte, properly adv. of s[=e]fte, adj.; akin to OS.
   s[=a]fto, adv., D. zacht, OHG. samfto, adv., semfti, adj., G.
   sanft, LG. sacht; of uncertain origin.]
   1. Easily yielding to pressure; easily impressed, molded, or
      cut; not firm in resisting; impressible; yielding; also,
      malleable; -- opposed to hard; as, a soft bed; a soft
      peach; soft earth; soft wood or metal.
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   2. Not rough, rugged, or harsh to the touch; smooth;
      delicate; fine; as, soft silk; a soft skin.
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            They that wear soft clothing are in king's houses.
                                                  --Matt. xi. 8.
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   3. Hence, agreeable to feel, taste, or inhale; not irritating
      to the tissues; as, a soft liniment; soft wines. "The
      soft, delicious air." --Milton.
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   4. Not harsh or offensive to the sight; not glaring; pleasing
      to the eye; not exciting by intensity of color or violent
      contrast; as, soft hues or tints.
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            The sun, shining upon the upper part of the clouds .
            . . made the softest lights imaginable. --Sir T.
                                                  Browne.
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   5. Not harsh or rough in sound; gentle and pleasing to the
      ear; flowing; as, soft whispers of music.
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            Her voice was ever soft,
            Gentle, and low, -- an excellent thing in woman.
                                                  --Shak.
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            Soft were my numbers; who could take offense?
                                                  --Pope.
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   6. Easily yielding; susceptible to influence; flexible;
      gentle; kind.
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            I would to God my heart were flint, like Edward's;
            Or Edward's soft and pitiful, like mine. --Shak.
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            The meek or soft shall inherit the earth. --Tyndale.
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   7. Expressing gentleness, tenderness, or the like; mild;
      conciliatory; courteous; kind; as, soft eyes.
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            A soft answer turneth away wrath.     --Prov. xv. 1.
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            A face with gladness overspread,
            Soft smiles, by human kindness bred.  --Wordsworth.
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   8. Effeminate; not courageous or manly, weak.
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            A longing after sensual pleasures is a dissolution
            of the spirit of a man, and makes it loose, soft,
            and wandering.                        --Jer. Taylor.
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   9. Gentle in action or motion; easy.
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            On her soft axle, white she paces even,
            And bears thee soft with the smooth air along.
                                                  --Milton.
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   10. Weak in character; impressible.
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             The deceiver soon found this soft place of Adam's.
                                                  --Glanvill.
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   11. Somewhat weak in intellect. [Colloq.]
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             He made soft fellows stark noddies, and such as
             were foolish quite mad.              --Burton.
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   12. Quiet; undisturbed; paceful; as, soft slumbers.
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   13. Having, or consisting of, a gentle curve or curves; not
       angular or abrupt; as, soft outlines.
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   14. Not tinged with mineral salts; adapted to decompose soap;
       as, soft water is the best for washing.
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   15. (Phonetics)
       (a) Applied to a palatal, a sibilant, or a dental
           consonant (as g in gem, c in cent, etc.) as
           distinguished from a guttural mute (as g in go, c in
           cone, etc.); -- opposed to hard.
       (b) Belonging to the class of sonant elements as
           distinguished from the surd, and considered as
           involving less force in utterance; as, b, d, g, z, v,
           etc., in contrast with p, t, k, s, f, etc.
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   Soft clam (Zool.), the common or long clam (Mya
      arenaria). See Mya.

   Soft coal, bituminous coal, as distinguished from
      anthracite, or hard, coal.

   Soft crab (Zool.), any crab which has recently shed its
      shell.

   Soft dorsal (Zool.), the posterior part of the dorsal fin
      of fishes when supported by soft rays.

   Soft grass. (Bot.) See Velvet grass.

   Soft money, paper money, as distinguished from coin, or
      hard money. [Colloq. U.S.]

   Soft mute. (Phonetics) See Media.

   Soft palate. See the Note under Palate.

   Soft ray (Zool.), a fin ray which is articulated and
      usually branched.

   Soft soap. See under Soap.

   Soft-tack, leavened bread, as distinguished from
      hard-tack, or ship bread.

   Soft tortoise (Zool.), any river tortoise of the genus
      Trionyx. See Trionyx.
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WordNet (r) 3.0 (2006):

soft coal
    n 1: rich in tarry hydrocarbons; burns readily with a smoky
         yellow flame [syn: bituminous coal, soft coal]