What is the origin of sanguine?
Sanguine comes from the Middle English adjective and noun sanguyn(e), sanguyn(e) “blood red, blood-red cloth, rosy hue, ruddy (of complexion), dominated by the humor blood, the humor blood.” The Middle English forms come from the Old French adjective sanguin(e), from the Latin adjective sanguineus “crimson, bloody, bloodstained. polluted with blood,” a derivative adjective of sanguis (stem sanguin-) “blood.” Neither sanguis nor sanguineus has any sense of the humor blood, which in medieval physiology is one of the four elemental fluids of the body (blood, phlegm, black bile, and yellow bile) regarded as determining, by their relative proportions, a person’s physical and mental constitution (their complexion). The medieval physiological theory actually dates back at least as far as Hippocrates, the “Father of Medicine,” (c460–375 b.c.); it was adopted by Galen (c129–216 a.d.), the Greek physician and medical writer and afterward by Muslim and medieval scholars. Sanguine entered English in the 14th century.