The waterfall model is a commonly used development methodology in software engineering, but there are several synonyms that describe similar approaches. One such approach is the traditional model, which also follows a structured, step-by-step process. The V-model is another synonym, which focuses on testing and verification throughout the development cycle. Similarly, the iterative model is a synonym that breaks down development into smaller, iterative cycles rather than one long, sequential process. The spiral model is a synonym that emphasizes risk management and flexibility in each iteration. Ultimately, while each methodology has its differences, they all aim to provide structure and organization to software development projects.