Where did the word "atom" come from?

The term "atom" comes from the Greek word for indivisible, because it was once thought that atoms were the smallest things in the universe and could not be divided. We now know that atoms are made up of three particles: protons, neutrons and electrons — which are composed of even smaller particles, such as quarks. An atom is the basic unit of an element. Less scientifically, the word atom can also mean a very small piece of anything at all. ... The Greek root of atom is atomos, which means "indivisible," since the scientists who first gave the atom its name imagined it couldn't be split or divided into smaller pieces. Democritus was a Greek philosopher who was the first person to use the term atom (atomos: meaning indivisible).