means a deep, lingering sadness or pensive sorrow, often with no clear cause and carrying a strange, reflective sweetness.

from From Greek melankholia, literally 'black bile' — melas (black) plus khole (bile). Ancient and medieval medicine held that the body ran on four humors, and an excess of black bile was thought to steep a person in gloom and brooding. The fluid was imaginary, but the word outlived the theory, carrying its dark, heavy color into English through Latin and Old French by the late Middle Ages.