A purebred horse of a breed developed for racing, with ancestry traceable to Arabian stallions. By extension, someone or something of superior breeding, training, or quality.
From thorough (Middle English thorou, meaning 'complete') + bred (past participle of breed). Originally meant 'completely bred' or 'bred through and through,' emphasizing the completeness of the breeding process. The specific horse breed sense developed in the 18th century.
Every modern Thoroughbred racehorse can trace its lineage back to just three Arabian stallions imported to England in the late 17th and early 18th centuries: the Byerley Turk, Darley Arabian, and Godolphin Arabian. This incredible genetic bottleneck means that despite centuries of selective breeding, all Thoroughbreds share a remarkably narrow genetic base, making them both exceptionally fast and somewhat genetically vulnerable.
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