thor·ough·bred / ˈ[unvoicedth]ərəˌbred/ • adj. (of a horse) of pure breed, esp. of a breed originating from English mares and Arab stallions and widely used as racehorses. ∎ inf. of outstanding quality: this thoroughbred car affords the luxury of three spoilers.• n. a horse of a thoroughbred breed. ∎ inf. an outstanding or first-class person or thing: this is a real thoroughbred of a record.