What does the root word "atom" mean and why is that not an accurate name

The concept of the atom originated round 440 BC. Leucippus of Miletus came up with the idea ... Atoms were impenetrably hard, meaning they could not be divided. In Greek, the prefix "a" means "not" and the word "tomos" means cut. Our word atom therefore comes from atomos, a Greek word meaning uncuttable.

And its not accurate because, we in fact, have split an atom.