Synonyms for the term "next-day" include "following day," "subsequent day," "tomorrow," and "day after." These words can be used to refer to the day immediately following the current one. Another synonym for "next-day" is "future," which can be used to refer to events that will occur at a later time. The term "upcoming" can also be used to describe the future, although it may not necessarily refer to the following day specifically. Regardless of which synonym is used, each word conveys the notion of time progressing and moving forward to the next point in time.