early 15c., "proportioned mixture of elements," from L. 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.