Explain why the word "atom" was an appropriate term for Democritus to choose?

Democritus was a pre-Socratic philosopher famous for first proposing that everything was made up of "atoms". The word atom comes from the Greek "atomos" which loosely translates as "indivisible". According to his theory, atoms were the basic constituents of all material things. Democritus suggested that if one attempted to break things down to their most basic elements one would eventually reach a point where there would be an "indivisible" element, an atom. He was a materialist in philosophical terms, and suggested everything was made up of "atoms and the void". Matter and space.
In this sense Democritus is a kind of proto-scientific thinker, and was influential with other famous materialists like the Roman Lucretius, who wrote about the atomic theory in his poem "De rerum natura" (On the Nature of Things).
The atomic theory resurfaced in the modern context with the chemist John Dalton in the early 19th century and became more refined in the late 19th with the discovery of the electron by J.J. Thomson and further developments of atomic physics in the 20th century.
https://en.wikipedia.org/wiki/Atom

Democritus's view was that everything was composed of "atoms," which, he thought, were indivisible particles. The term "atom" comes from the Greek word "tomos," which means "slice" or "section." (Consider the meaning of other words that contain root "tom," such as "tomography.") The prefix "a" indicates negation, or opposite of what follows. (Again, think of some words with Greek roots that begin with "a.") Thus, the term "atom" is an appropriate name for a particle that cannot be broken up into smaller pieces. Democritus' theory stated that there are different kinds of atoms (which form different kinds of matter), that they are in constant motion, and there is empty space between them.
The contemporary atomic theory of matter, confirmed by numerous experiments, agrees with most of these assumptions: matter is in fact composed of atoms, there is empty space between them, and atoms are constantly moving or vibrating. Of course, we know now that an atom is not the smallest constituent of matter, as was once assumed. An atom itself consists mostly of empty space, with nucleus (containing protons and neutrons) in the center and electrons orbiting around it. The electrons, protons and neutrons are called "elementary" particles, which implies that they cannot be broken down further. However, the protons and neutrons are theorized to consist of even smaller pieces, called quarks.
https://en.wikibooks.org/wiki/General_Chemistry/Atomic_Structure/History_of_Atomic_Structure