Melancholy (noun)

1. A feeling of pensive sadness, typically with no obvious cause.
2. A feeling of sadness, pensiveness, or depression.
3. A feeling of dejection, sorrow or forlornness.

Origin:

Late middle english: via old french from latin melancholia, from greek melankholia, from melas, melan- "black" + kholē "bile" (formerly believed to be a cause of depression). the word originally denoted a disorder characterized by abnormal amounts of black bile in the body; the sense "gloomy state of mind" dates from the early 17th century.

Examples:

1. She felt a sense of melancholy as she thought about her past.
2. The music had a melancholy tone.
3. The gloomy weather added to the melancholy atmosphere.
4. The painting had a melancholic subject matter.
5. The melancholic mood of the poem reflects the poet's feelings.