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early 15c., "proportioned mixture of elements," from Latin temperamentum "proper mixture," from temperare "to mix" (see temper). In medieval theory, it meant a combination of qualities (hot, cold, moist, dry) that determined the nature of an organism; this was extended to a combination of the four humors (sanguine, choleric, phlegmatic, and melancholic) that made up a person's characteristic disposition. General sense of "habit of mind, natural disposition" is from 1821.
temperament tem·per·a·ment (těm'prə-mənt, těm'pər-ə-)
The manner of thinking, behaving, or reacting characteristic of a specific person.