1. stone (of a fruit); pit; pip
2. core (of an organization, team, etc.); nucleus; heart
それこそが、この物語の核なのだとわかった。I realized that this was the very core of the story.
3. nuclear weapons
世界から核をなくしたい。I want to rid the world of nuclear weapons.
4. nucleus (of an atom)
核の周りを電子が回っている。Electrons orbit around the nucleus.
5. nucleus (of a cell)
6. condensation nucleus
7. (planetary) core
地球の核は主に鉄でできている。The Earth's core is made mostly of iron.
8. ring (in a cyclic compound)
9. kernel; core
10. nucleus (of a cultured pearl)