late 15c. (late 13c. as a surname), from black (adj.) + bird (n.1). Originally in reference to a large species of European thrush, the male of which is wholly black; applied in the New World to other similar birds. OED says so called for being the only "black" (really dark brown) bird among the songbirds, reflecting an older sense of bird that did not include rooks, crows, or ravens.