The term "melancholia" comes from the Greek words melas (μέλας), meaning "black," and kholé (χολή), meaning "bile". Literally translating to "black bile," the word originally described a medical condition believed by ancient Greeks to be caused by an excess of this humor, which they associated with sadness, irritability, and a gloomy disposition. The term entered English via Late Latin, melancholia, and Old French, melancolie, and while its meaning evolved from its humoral origins, it retained the association with a deeply negative and persistent state of mind.  The term 'melancholia' first appears in On the Sacred Disease- a medical text attributed to Hippocrates from approximately 400 B.C. This book recognizes the 'sorrows, griefs, despondency, and lamentations' associated with the melancholy condition.  Shift in meaning: As understanding of the humors declined, especially after the 18th century, the term "melancholia" evolved to describe a gloomy mental state rather than a literal imbalance of bile.  Modern Usage: Today, the word is less common as a clinical term, with "depression" and other mood disorder terms taking its place, but it still carries its historical weight of profound sadness and gloom. 

Melancholy describes a pensive, thoughtful mood that involves deep, often quiet sadness or gloominess.  It can be an intense feeling of sadness evoked by something, such as the melancholy cries of sheep, or a general tendency to be thoughtful and sad. While related to sadness, melancholy is more complex, often incorporating themes of nostalgia, longing, or a reflective, introverted state. 

According to the Oxford English Dictionary (OED), the noun melancholia was first used in Middle English before 1398.  The dictionary cites an appearance in a translation by John Trevisa, a translator who was active before 1398.  According to the Oxford English Dictionary (OED), the word "melancholy" first appeared in English in the Middle English period, with early evidence of its use as both an adjective and a noun dating back to the late 14th century. The earliest recorded evidence for the adjective and noun is from a1393. 

Examples of "melancholia" used in English:  
"He has such a sparkle in his eye, and a joyful face, but he had a lot of melancholia."  
"After his wife left, he fell into a deep, inexplicable melancholia." 
"The music created a sense of melancholia as the characters anticipated their inevitable separation." 
"And people looking for a dose of introspective melancholia at the end of the festival will have to choose between The National on the Other Stage, and James Blake, who plays in the Woodsies tent." 

Examples of "melancholy" used in a sentence: 
"I was deeply aware of his melancholy as he stood among the mourners." 
"The general watched the process with an air of melancholy."
"It was in these hours of the late afternoon that Tom Mulligan felt most melancholy."
"He fixed me with those luminous, empty eyes and his melancholy smile."