any of several small North American songbirds of the genus Sialia, having predominantly blue plumage, as the eastern S. sialis,which has a blue back and a reddish-brown breast.
1680s, N.Amer. warbler-like bird, from blue in reference to its plumage + bird. Figurative use in bluebird of happiness is from 1909 play romance "l'Oiseau bleu," lit. "The Blue Bird," by Belgian dramatist and poet Maurice Maeterlinck (1862-1949).