By the day means daily or on a daily basis. Synonyms for this phrase include day by day, each day, daily, every day, per day, and on a daily basis. It is a common phrase used in various contexts such as in business, finance, and personal life when referring to something that happens every day or changes frequently. For instance, someone might say, "The cost of living is getting higher by the day" or "The number of COVID-19 cases is increasing day by day." Using synonyms for "by the day" can make your language more varied and engaging while still communicating the same idea.