As is suggested in the entry OPTIMIST, optimistic, an adjective, means "inclined or disposed to take a favorable view of life." Sanguine has the somewhat related meanings of "cheerful," "confident," "hopeful": "He is a lively, sanguine person." (Sanguine, derived from a Latin term meaning "bloody," has acquired its present meaning because, in medieval physiology, ruddy-faced people were considered healthy, animated, spirited, and buoyant.) Sanguine is a more precise word than optimistic, which is overused. In a sentence such as "Tom is not optimistic about bis chances for leaving early," either sanguine or hopeful might replace optimistic.
Dictionary of problem words and expressions. Harry Shaw. 1975.