What does "protium" mean?

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.

What is a synonym for "protium"?

Common synonyms include: isobar, isomer.

/ˈpɹoʊ.tiəm/ noun

noun ·Rare ·Advanced level

Noun

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."

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

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