protium

noun

Etymology: From proto- + -ium. From Ancient Greek πρῶτος (prôtos, “first”).

1. The lightest and most common isotope of hydrogen, having a single proton and no neutrons: 11H. It is the only stable nuclide with no neutrons.

   “So far there are no differences among the protiums extracted at various labs, except for concentration levels.”

2. An atom of this isotope.

   “This radioactive decay leaves behind a protium as well.”