The Collaborative International Dictionary of English v.0.48:

Softening \Sof"ten*ing\,
   a. & n. from Soften, v.
   [1913 Webster]

   Softening of the brain, or Cerebral softening (Med.), a
      localized softening of the brain substance, due to
      hemorrhage or inflammation. Three varieties, distinguished
      by their color and representing different stages of the
      morbid process, are known respectively as red, yellow, and
      white, softening.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Soften \Sof"ten\, v. t. [imp. & p. p. Softened; p. pr. & vb.
   n. Softening.]
   To make soft or more soft. Specifically:
   [1913 Webster]
   (a) To render less hard; -- said of matter.
       [1913 Webster]

             Their arrow's point they soften in the flame.
                                                  --Gay.
       [1913 Webster]
   (b) To mollify; to make less fierce or intractable.
       [1913 Webster]

             Diffidence conciliates the proud, and softens the
             severe.                              --Rambler.
       [1913 Webster]
   (c) To palliate; to represent as less enormous; as, to soften
       a fault.
       [1913 Webster]
   (d) To compose; to mitigate; to assuage.
       [1913 Webster]

             Music can soften pain to ease.       --Pope.
       [1913 Webster]
   (e) To make calm and placid.
       [1913 Webster]

             All that cheers or softens life.     --Pope.
       [1913 Webster]
   (f) To make less harsh, less rude, less offensive, or less
       violent, or to render of an opposite quality.
       [1913 Webster]

             He bore his great commision in his look,
             But tempered awe, and softened all he spoke.
                                                  --Dryden.
       [1913 Webster]
   (g) To make less glaring; to tone down; as, to soften the
       coloring of a picture.
       [1913 Webster]
   (h) To make tender; to make effeminate; to enervate; as,
       troops softened by luxury.
       [1913 Webster]
   (i) To make less harsh or grating, or of a quality the
       opposite; as, to soften the voice.
       [1913 Webster]

WordNet (r) 3.0 (2006):

softening
    adj 1: having a softening or soothing effect especially to the
           skin [syn: demulcent, emollient, salving,
           softening]
    n 1: the process of becoming softer; "refrigeration delayed the
         softening of the fruit"; "he observed the softening of iron
         by heat"

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "softening":
   abatement, abating, allaying, allayment, alleviating, alleviation,
   alleviative, allowance, altering, analgesia, analgesic, anesthesia,
   anesthetic, anesthetizing, anodyne, appeasement, assuagement,
   assuaging, assuasive, attenuation, attrition, balmy, balsamic,
   benumbing, blunting, bounding, calming, cathartic, chastening,
   cleansing, color, cushioning, dampening, damping, deadening,
   debilitation, decontamination, demulcent, demulsion,
   devitalization, dilution, diminishing, diminishment, diminution,
   dulcification, dulling, ease, easement, easing, effemination,
   emollient, enervation, enfeeblement, evisceration, exhaustion,
   extenuating, extenuating circumstances, extenuation, extenuative,
   extenuatory, falling-off, fatigue, gilding, gloss, hushing,
   inanition, languishment, laxation, leniency, lenitive, lessening,
   letdown, letup, lightening, limitative, limiting, loosening,
   lulling, mellowing, mitigating, mitigation, mitigative, mitigatory,
   modificatory, modifying, modulation, modulatory, mollification,
   mollifying, numbing, pacification, padding, pain-killing,
   palliation, palliative, purgative, qualification, qualificative,
   qualificatory, qualifying, quietening, quieting, reducing,
   reduction, relaxation, relaxing, relief, relieving, remedial,
   remedy, remission, restricting, restrictive, salving, slackening,
   softening-up, soothing, subduement, subduing, tempering, thinning,
   tranquilization, varnish, weakening, whitewash, whitewashing