coeternal

adjective

co·​eter·​nal ˌkō-i-ˈtər-nᵊl 

: equally or jointly eternal

… the old 19th-century view that … if life and matter are coeternal, there is no problem of the origin of life to be figured out.

—Carl Sagan

coeternally adverb

existing coeternally

coeternity noun

Word History

Etymology

Middle English, borrowed from Late Latin coaeternālis, from Latin co- co- + Late Latin aeternālis eternal entry 1, after coaeternus "coeternal"

First Known Use

14th century, in the meaning defined above