melancholyyoudaoicibaDictgodict[melancholy 词源字典]
melancholy: [14] Etymologically, melancholy means ‘black gall’. The word comes via Old French melancolie and late Latin melancholia from Greek melagkholíā, a compound formed from mélās ‘black’ (source also of English melanin [19] and melanoma [19]) and kholé ‘bile’ (a relative of English gall). This ‘black bile’ was one of the four bodily substances or ‘humours’ whose relative preponderance, according to medieval medical theory, determined a person’s physical and mental state. Excess of black bile was thought to cause depression – hence the modern meaning of melancholy.
=> gall, melanoma[melancholy etymology, melancholy origin, 英语词源]
melancholy (n.)youdaoicibaDictgodict
c. 1300, "condition characterized by sullenness, gloom, irritability," from Old French melancolie "black bile, ill disposition, anger, annoyance" (13c.), from Late Latin melancholia, from Greek melankholia "sadness," literally (excess of) "black bile," from melas (genitive melanos) "black" (see melanin) + khole "bile" (see Chloe). Medieval physiology attributed depression to excess of "black bile," a secretion of the spleen and one of the body's four "humors."

The Latin word also is the source of Spanish melancolia, Italian melancolia, German Melancholie, Danish melankoli, etc. Old French variant malencolie (also in Middle English) is by false association with mal "sickness."
melancholy (adj.)youdaoicibaDictgodict
late 14c., "with or caused by black bile; sullen, gloomy, sad," from melancholy (n.); sense of "deplorable" (of a fact or state of things) is from 1710.