What is the meaning of melancholy?

noun

• A feeling of thoughtful sadness.
• A constitutional tendency to be gloomy and depressed.
• A humor that was once believed to be secreted by the kidneys or spleen and to cause sadness and melancholy.
  • synonyms: black bile

adjective

• Characterized by or causing or expressing sadness.
  • usage: "growing more melancholy every hour"; "her melancholic smile"; "we acquainted him with the melancholy truth"
  • synonyms: melancholic
• Grave or even gloomy in character.
  • usage: "solemn and mournful music"; "a suit of somber black"; "a somber mood"
  • synonyms: somber, sombre