The Top 10 Relationship Words That Aren't Translatable Into English | Marriage 3.0 | Big Think: Retrouvailles (French): The happiness of meeting again after a long time.
This is such a basic concept, and so familiar to the growing ranks of commuter relationships, or to a relationship of lovers, who see each other only periodically for intense bursts of pleasure. I’m surprised we don’t have any equivalent word for this subset of relationship bliss. It’s a handy one for modern life.