The term "passing fashion" can be replaced by several synonyms that are often used interchangeably. One popular synonym is "fad," which refers to a trend that gains popularity quickly and fades away just as quickly. Another similar term is "trend," which refers to a popular style or behavior that has a more extended lifespan but still eventually fades away. "Fleeting fashion" is also a synonym for passing fashion that emphasizes the short-lived nature of the trend. "Transient style" and "ephemeral trend" are more formal synonyms that convey the same meaning. Ultimately, each of these synonyms provides an alternative way of referring to something that is currently popular but expected to fade away in the near future.