Source : Webster's Revised Unabridged Dictionary (1913)

Soften \Sof"ten\, v. i.
   To become soft or softened, or less rude, harsh, severe, or
   obdurate.

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

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

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

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

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

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

Source : WordNet®

soften
     v 1: make (images or sounds) soft or softer [ant: {sharpen}]
     2: lessen in force or effect; "soften a shock"; "break a fall"
        [syn: {dampen}, {damp}, {weaken}, {break}]
     3: give in, as to influence or pressure [syn: {yield}, {relent}]
        [ant: {stand}]
     4: protect from impact; "cushion the blow" [syn: {cushion}, {buffer}]
     5: make less severe or harsh; "He moderated his tone when the
        students burst out in tears" [syn: {mince}, {moderate}]
     6: make soft or softer; "This liquid will soften your laundry"
        [ant: {harden}]
     7: become soft or softer; "The bread will soften if you pour
        some liquid on it" [ant: {harden}]