There are a variety of synonyms for the phrase "once a day" that can be used to make your language more varied and engaging. For instance, you might use "daily," "every day," "per diem," "24 hours apart," or "once per diurnal cycle." Each of these phrases has its own unique rhythm and connotations that can add depth and texture to your writing. Whether you're creating a blog post or crafting a professional document, incorporating synonyms for common phrases is a great way to keep your audience engaged and interested. With a little creativity and attention to detail, you can improve the quality and impact of your writing and communication.