sadden

from The American Heritage® Dictionary of the English Language, 5th Edition.

• transitive & intransitive verb To make or become sad.

from The Century Dictionary.

• To become heavy, compact, or firm; harden, as land or roads after a thaw or rain.
• To become sad or sorrowful.
• To make compact; make heavy or firm; harden.
• To make sad; depress; make gloomy or melancholy.
• To make dark-colored; specifically, in dyeing and calico-printing, to tone down or shade (the colors employed) by the application of certain agents, as salts of iron, copper, or bichromate of potash.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To become, or be made, sad.
• transitive verb obsolete To render heavy or cohesive.
• transitive verb To make dull- or sad-colored, as cloth.
• transitive verb To make grave or serious; to make melancholy or sorrowful.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb To make sad or unhappy.
• verb intransitive, rare To become sad or unhappy.
• verb rare To darken a color during dyeing

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb make unhappy
• verb come to feel sad