" ""Siamese cat"" is capitalised, whilst ""house cat"" is not. You made one of the best points that I saw during the ""Genesis Creation myth"" debate; that whilst ""myth"" was technically correct, it was misleading, as the public generally understands myth to mean false. Extremely different scenario; exact same analogy. ""Thoroughbred"", in most cases, including racehorses, is referring to a purebred horse, and not a specific breed."