WordNet sense 1 (a humor that was once believed to be secreted by the kidneys or spleen and to cause sadness and melancholy):

black bile

WordNet sense 2 (characterized by or causing or expressing sadness):

melancholic

WordNet sense 3 (experiencing or showing sorrow or unhappiness):

sad

WordNet sense 4 (grave or even gloomy in character):

somber, sombre

WordNet sense 5 (lacking cheer; depressing):

uncheerful