Reunion
Part of speech: noun
Definition: The process or act of reuniting. A planned event at which members of a dispersed group meet together.
Example sentence: The Guns N' Roses reunion didn't happen by chance or whatever. It was always looked at as a possibility, but it never seemed right or felt right.
Reunification
Part of speech: noun
Definition: The unification of something that was previously divided; used especially of a country
Example sentence: Over a period of 20 years, German reunification has cost 2 trillion euros, or an average of 100 billion euros a year. So, we have to ask ourselves: Aren't we willing to pay a tenth of that over several years for Europe's unity?