Septennial is a word that refers to something that occurs every seven years. However, there are a number of synonyms that can be used instead of septennial. One option is "heptennial," which also means occurring every seven years. Another synonym is "septiform," which refers to having the shape of a septenary or being divided into seven parts. Additionally, the word "septenary" can be used to describe something that relates to the number seven or a group of seven. Other possible synonyms for septennial might include "seven-year-cycle," "seven-year-periodicity," or simply "seven-year." With so many options, it's easy to find the right word to use in place of septennial.