As nouns,
plutonium 239 is a hyponym of
Pu; that is,
plutonium 239 is a
word with a more specific, narrower meaning than
Pu:
- Pu: a solid silvery grey radioactive transuranic element whose atoms can be split when bombarded with neutrons; found in minute quantities in uranium ores but is usually synthesized in nuclear reactors; 13 isotopes are known with the most important being plutonium 239
- plutonium 239: a highly fissionable isotope of plutonium that is used in atomic weapons and as a reactor fuel; produced by irradiating uranium 238 with slow electrons