Source : Webster's Revised Unabridged Dictionary (1913)

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.]

             Marl is binding, and saddening of land is the great
             prejudice it doth to clay lands.     --Mortimer.
   (b) To make dull- or sad-colored, as cloth.
   (c) To make grave or serious; to make melancholy or
       sorrowful.

             Her gloomy presence saddens all the scene. --Pope.

Sadden \Sad"den\, v. i.
   To become, or be made, sad. --Tennyson.

Source : WordNet®

sadden
     v 1: make unhappy; `The news of her death saddened me' [ant: {gladden}]
     2: come to feel sad [ant: {gladden}]