melancholia
definition
a deep, persistent sadness or gloom often without a specific cause
example
After the long winter months, a sense of melancholia settled over the town, leaving its residents feeling inexplicably heavy-hearted.
synonyms
sadness,gloom,despondency
word origin — Derived from the Greek word 'melankholía', which means 'black bile', one of the four humors in ancient medicine associated with a melancholic temperament.