πρῶτον

The Greek word proton (πρῶτον) means 'first' or 'first thing'—neuter form of protos. When Rutherford discovered the positively charged nucleus of the atom in 1909, he had no idea what it was made of. He knew atoms contained electrons. He knew those electrons were negative. So what was positive at the center?

By 1919, Rutherford proved that bombarding nitrogen atoms with alpha particles produced hydrogen nuclei. In 1920, addressing the Royal Society, he proposed calling this positively charged nucleus the proton. He chose a Greek word to match the naming convention of the newly discovered electron.

The proton sat quietly in physics textbooks for twelve years. Then in 1932, James Chadwick discovered the neutron—an uncharged particle with almost identical mass to the proton. Suddenly atoms had a comprehensible architecture: protons in the nucleus, electrons orbiting, neutrons as neutral ballast.

The word proton is now synonymous with fundamental. We speak of proton therapy for cancer, proton beams, the proton gradient that powers cellular energy. But the word itself is just ancient Greek for 'first thing'—the name Rutherford gave to the thing that came before everything else.