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

sadden \sad"den\, v. t. imp.  p. p. saddened; p. pr.  vb.
   n. saddening.
   to make sad. specifically:
   a to render heavy or cohesive. obs.
       1913 webster

             marl is binding, and saddening of land is the great
             prejudice it doth to clay lands.     --mortimer.
       1913 webster
   b to make dull- or sad-colored, as cloth.
   c to make grave or serious; to make melancholy or
       sorrowful.
       1913 webster

             her gloomy presence saddens all the scene. --pope.
       1913 webster
see also:
saddened saddening 

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

sadden \sad"den\, v. i.
   to become, or be made, sad. --tennyson.
   1913 webster

[3] : WordNet (r) 2.0

sadden
     v 1: make unhappy; `the news of her death saddened me' ant: gladden
     2: come to feel sad ant: gladden
see also:
gladden 

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

33 moby thesaurus words for "sadden":
   affect, aggrieve, beat down, cast down, damp, dampen,
   dampen the spirits, darken, dash, deject, depress, discourage,
   dishearten, dispirit, distress, grieve, knock down, lower,
   lower the spirits, melt, melt the heart, move, oppress, press,
   press down, reach, sink, soften, sorrow, touch, weigh down,
   weigh heavy upon, weigh upon

Sadden >> S Words
Sadden, definition of term: Sadden
sadden_pag1.html