Melancholic, melancholy, atrabilious, hypochondriac are comparable when they mean gloomy or depressed, especially as a manifestation of one's temperament or state-of-health.
Melancholic and melancholy are often used interchangeably without additional implications or suggestions, although each can be used discriminatingly to suggest the differences inherent in their related nouns (see melancholia under SADNESS ), (see melancholy under SADNESS ).
In such use melancholic describes a person who is afflicted with or inclined to melancholia.
Melancholy, on the other hand, describes a person, or the mood, disposition, acts, or utterances of a person, who is excessively sad or detached in spirit and, usually, averse to what is cheerful or gay.
Atrabilious preserves the implication of an unhealthy physical condition more strongly than the preceding words; often in modern use it suggests the morose or choleric disposition of the dyspeptic or the predilection for gloom of those who have been subjected to severe strain.
Hypochondriac comes close to atrabilious in its suggestion of constitutional gloominess but it implies also an unwholesome anxiety about one's state of health.