melancholy

The word melancholy is used both as a noun and as an adjective and you can use the word for a very deep feeling of sadness. Usually the word is used for a kind of sadness the reason of which is hard to explain and the feeling also lasts for a long time. The following sentence can make the meaning of the word quite clear as it is used in the context to make you understand well: Though we had all the facilities available to enjoy, an indescribable feeling of melancholy descended over us.