The word "primigenous" is not a very common word, and it may be helpful to know some synonyms for it. "Primordial" is a similar word that means existing from the very beginning. "Ancient" and "prehistoric" both describe things that existed a long time ago. "Antediluvian" refers specifically to the time before the biblical flood. "Protohistoric" is used to describe a time period where there are some written records, but they are not fully developed. "Ur-" is a prefix that can be added to other words to mean ancient or original. By using these synonyms, you can enhance your language and make it more diverse and interesting.