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melancholy (n.)[melancholy 词源字典]: 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 etymology, melancholy origin, 英语词源]
sullen (adj.): 1570s, alteration of Middle English soleyn "unique, singular," from Anglo-French *solein, formed on the pattern of Old French solain "lonely," from soul "single," from Latin solus "by oneself, alone" (see sole (adj.)). The sense shift in Middle English from "solitary" to "morose" (i.e. "remaining alone through ill-humor") occurred late 14c. Related: Sullenly; sullenness.