One who rules in place of the monarch, especially because the monarch is too young, absent, or disabled. [from 15th c.]
(now chiefly historical) A member of a municipal or civic body of governors, especially in certain European cities. [from 16th c.]
(Scotland, Canada, US) A member of governing board of a college or university; also a governor of the Smithsonian Institute in Washington DC. [from 18th c.]