Fly by is a commonly used phrase that refers to something passing quickly or swiftly. However, there are several synonyms for fly by that can be used to add variety and specificity to your language. Some possible options include zip by, streak past, dart past, whiz by, skim over, breeze by, swoop past, and rush past. These terms indicate different levels of speed and motion, allowing you to convey a more vivid and descriptive image of the action. Using synonyms for fly by can also help to prevent repetition in your writing, making your prose more dynamic and engaging.