Definition of royal highness in English English dictionary
politeness Expressions such as Your Royal Highness and Their Royal Highnesses are used to address or refer to members of royal families who are not kings or queens. your/his/her Royal Highness used when speaking about or to a royal person, especially a prince or princess
any person who is a member of a royal family; title given to members of a royal family; title that was used before 1917 designating any family member (such as brother, sister, child, grandchild, aunt or uncle) who belonged to the male descendant of the royal family (England); title used since 1917 designating child or grandchild of the monarch (England); any person who is given this title by Royal family (England)