Septimal is an adjective that refers to something that is related to the number seven. It is a rather uncommon word, and there are only a few synonyms to describe this concept, such as "related to septenary," "seventh," or "heptadic." Other possible synonyms could be "sevenfold," "seven-based," or "septenary." These words all convey a similar meaning, which is to describe something that is related to or derived from the number seven. While the word septimal may not be used frequently, these synonyms can be useful when trying to describe something related to the number seven or a seventh part.