sanguis

Sanguis is the Latin word for blood. It is the root of several English terms, including sanguine, sanguinary, and sanguineous, and is closely related to sangre in Spanish and sang in French.

In physiology, blood is the circulating fluid that carries oxygen and nutrients, removes carbon dioxide and wastes, and supports immune defense and clotting. Human blood comprises plasma, red blood cells, white blood cells, and platelets.

In ancient medicine, the theory of the four humors linked blood (sanguine) to a warm, moist temperament. Although this framework is obsolete, the term sanguine survives in language to describe optimism or confidence.

Sanguine also names a drawing material—reddish-brown chalk used in figure drawing—and a color term for blood-red hues. The related form sangfroid comes from French and means calmness in danger.

Today, sanguis is primarily encountered as a historical or linguistic term; modern science uses "blood" for the bodily fluid, while the adjective sanguine remains common in literature and everyday speech.