The word "speedest" is a superlative form of "speedy," which means moving or operating at a high rate of speed. Synonyms for "speedest" include "fastest," "quickest," "swiftest," and "most rapid." These words all convey a sense of urgency and efficiency, suggesting action that is nimble and energetic. Other synonyms for "speedest" might include "hastiest," "most expeditious," "most fleet-footed," or "most dizzying." Regardless of the word chosen, all of these synonyms capture the essence of swift or prompt movement, conveying a sense of motion that is both exciting and impressive.