san·guine / ˈsanggwin/ • adj. cheerfully optimistic: they are not sanguine about the prospect.• n. a blood-red color. ∎  a deep red-brown crayon or pencil containing iron oxide.DERIVATIVES: san·guine·ly adv.san·guine·ness n.

sanguine (in medieval science and medicine) of or having the constitution associated with the predominance of blood among the bodily humours, supposedly marked by a ruddy complexion and an optimistic disposition; the modern use of sanguine to mean cheerfully optimistic derives from this.

In heraldry, sanguine is the name for a blood-red stain used in blazoning.