coeval

Coeval comes to English from the Latin word coaevus, meaning "of the same age." Coaevus was formed by combining the co- prefix ("in or to the same degree") with Latin aevum ("age" or "lifetime"). The root aevum is also a base in such temporal words as longevity, medieval, and primeval. Although coeval can technically describe any two or more entities that coexist, it is most typically used to refer to things that have existed together for a very long time (such as galaxies) or that were concurrent with each other in the distant past (parallel historical periods of ancient civilizations, for example).