When it comes to describing something that is operating smoothly, there are many synonyms to choose from. These include seamlessly, effortlessly, faultlessly, fluently, perfectly, and efficiently. Smoothly can also be replaced with terms such as polished, refined, and suave to convey a sense of sophistication and elegance. Other options include silkily, slickly, and fluidly to describe something that moves or operates with ease. For a more natural tone, one could use phrases like "without a hitch" or "with no complications." Choosing the right synonym for smoothly largely depends on the context and desired tone of the description.