The phrase "royal line" refers to the lineage of kings and queens from a specific reigning family. However, there are many synonyms for this term that can describe this concept in different ways. Some options include "dynasty," emphasizing the line of rulers and their familial connections, and "monarchy," focusing on the system of government led by one ruler. Other terms that could be used include "regal family," "imperial bloodline," and "sovereign heritage." Depending on the context and tone, any of these synonyms could effectively communicate the idea of a powerful and influential family with a long history of ruling over a country or region.