Prokaryote

Etymology
Prokaryote:

pro: "before" (from greek πρό-, meaning "before")

karyon: "nut" (from greek καρυόν, meaning "nut" or "kernel")

Explanation
Prokaryotes are single-celled organisms that existed, evolutionarily, before (pro) the development of a nucleus, which is a somewhat kernel-shaped organelle (karyon).