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"blood-red," late 14c. (late 12c. as a surname), from Old French sanguin (fem. sanguine), from Latin sanguineus "of blood," also "bloody, bloodthirsty," from sanguis (genitive sanguinis) "blood" (see sanguinary). Meaning "cheerful, hopeful, confident" first attested c.1500, because these qualities were thought in medieval physiology to spring from an excess of blood as one of the four humors. Also in Middle English as a noun, "type of red cloth" (early 14c.).
sanguine san·guine (sāng'gwĭn)
Of a healthy, reddish color; ruddy.
Cheerfully confident; optimistic.
Having blood as the dominant humor in terms of medieval physiology.
Archaic Having the temperament and ruddy complexion that was formerly thought to be characteristic of a person dominated by this humor; passionate.
chalk or crayon drawing done in a blood-red, reddish, or flesh colouring. The pigment employed is usually a chalk or clay containing some form of iron oxide. Sanguine was used extensively by 15th- and 16th-century artists such as Leonardo da Vinci (who employed it in his sketches for the Last Supper), Michelangelo, Raphael, and Andrea del Sarto.