Relating to or characterized by melancholy or an excess of black bile in the ancient medical humoral theory.
From Latin atra bilis 'black bile' + -arian adjectival suffix. Extended form showing the same etymological root as other atrabil- words.
English borrowed so many medical terms from Latin humoral theory that we still use them—'sanguine,' 'choleric,' and 'phlegmatic' all refer to ancient temperament types.
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