Old English bredan "bring young to birth, carry," also "cherish, keep warm," from West Germanic *brodjan (cognates: Old High German bruoten, German brüten "to brood, hatch"), from *brod- "fetus, hatchling," from PIE *bhreue- "burn, heat" (see brood, n.). Original notion of the word was incubation, warming to hatch. Sense of "grow up, be reared" (in a clan, etc.) is late 14c. Related: Bred; breeding.

"race, lineage, stock" (originally of animals), 1550s, from breed, v.. Of persons, from 1590s. Meaning "kind, species" is from 1580s.