preatomic

pre·a·tom·ic

 (prē′ə-tŏm′ĭk)
adj.
Of or belonging to the time before the use of, existence of, or capability for atomic energy or weapons.

preatomic

(ˌpriːəˈtɒmɪk)
adj
occurring, existing or characteristic of the period before the atomic age

pre•a•tom•ic

(ˌpri əˈtɒm ɪk)

adj.
of or pertaining to the period of history preceding the atomic age.
[1945]