A racing mare is a female horse that has been trained specifically for racing. Synonyms for this term could include speedster mare, galloping mare, or even sprinting mare. All of these phrases capture the essence of a horse that is capable of running at high speeds over short distances, which is the primary requirement for success in the sport of horse racing. Other possible synonyms could include thoroughbred mare, champion mare, or purebred mare, which might be used to emphasize the quality of the animal's lineage and potential success on the track. Ultimately, there are many ways to describe a racing mare, depending on the specific traits or attributes that are most important to the context.