5 synonyms for the word "fast" with examples and explanations: 1. Quick - happening or done in a short time. Example: The quick fox jumped over the lazy dog. 2. Rapid - happening or done quickly, especially in a way that is noticeable or surprising. Example: The rapid spread of the disease was a cause for concern. 3. Speedy - moving or happening very quickly. Example: The speedy delivery service arrived with my package in no time. 4. Swift - moving or happening very quickly and smoothly. Example