[1] : The Collaborative International Dictionary of English v.0.48

sweeten \sweet"en\, v. t. imp.  p. p. sweetened; p. pr. 
   vb. n. sweetening. see sweet, a.
   1. to make sweet to the taste; as, to sweeten tea.
      1913 webster

   2. to make pleasing or grateful to the mind or feelings; as,
      to sweeten life; to sweeten friendship.
      1913 webster

   3. to make mild or kind; to soften; as, to sweeten the
      temper.
      1913 webster

   4. to make less painful or laborious; to relieve; as, to
      sweeten the cares of life. --dryden.
      1913 webster

            and sweeten every secret tear.        --keble.
      1913 webster

   5. to soften to the eye; to make delicate.
      1913 webster

            correggio has made his memory immortal by the
            strength he has given to his figures, and by
            sweetening his lights and shadows, and melting them
            into each other.                      --dryden.
      1913 webster

   6. to make pure and salubrious by destroying noxious matter;
      as, to sweeten rooms or apartments that have been
      infected; to sweeten the air.
      1913 webster

   7. to make warm and fertile; -- opposed to sour; as, to dry
      and sweeten soils.
      1913 webster

   8. to restore to purity; to free from taint; as, to sweeten
      water, butter, or meat.
      1913 webster
      1913 webster
see also:
sweetened sweetening sweet 

[2] : The Collaborative International Dictionary of English v.0.48

sweeten \sweet"en\, v. i.
   to become sweet. --bacon.
   1913 webster

[3] : WordNet (r) 2.0

sweeten
     v 1: make sweeter in taste syn: dulcify, edulcorate, dulcorate
          ant: sour
     2: make sweeter, more pleasant, or more agreeable; "sweeten a
        deal"
see also:
dulcify edulcorate dulcorate sour 

[4] : Moby Thesaurus II by Grady Ward, 1.0

60 moby thesaurus words for "sweeten":
   allay, alleviate, appease, assuage, bleach, bowdlerize, brighten,
   candy, clean, clean out, clean up, cleanse, clear out, conciliate,
   delouse, depurate, deterge, dress up, dry-clean, dulcify, dust,
   dust off, ease, edulcorate, embellish, embroider, expurgate,
   freshen, gild, gild the lily, glaze, honey, lighten, lustrate,
   mitigate, moderate, mollify, mull, palliate, placate, propitiate,
   purge, purify, reform, saccharify, scavenge, soften, spruce,
   steam-clean, sugar, sugar off, sugarcoat, sweep out, temper, tidy,
   whiten, wipe, wipe off, wipe out, wipe up

Sweeten >> S Words
Sweeten, definition of term: Sweeten
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