Sempiternity is a term often used to describe eternity or an endless duration of time. And while it is a beautiful word, there are several synonyms that can be used in its place. Perpetuity, infinity, unendingness, perpetuation, immortality, and ceaselessness are just a few examples. Each of these words carries a similar meaning to sempiternity, but may be more appropriate for different contexts. For example, perpetuity might be used to describe something that lasts forever, while infinity might be used to describe something that goes on without end. Whichever synonym is chosen, it will convey the idea of something that lasts forever, making it an ideal choice for grand, eternal themes.