There are many synonyms for the phrase "amazing speed." Some include the words rapid, swift, lightning-fast, expedited, and speedy. These words all convey a sense of incredible speed and urgency. Other synonymous phrases for amazing speed might include breakneck pace or blistering speed, which both suggest a pace so fast it may be dangerous. Another option could be supersonic speed, which implies a speed faster than the sound barrier. Whatever word or phrase you choose to describe amazing speed, it is clear that it is a phrase reserved for only the fastest of fast activities.