1.nounA political unit, typically having an extensive territory or comprising a number of territories or nations (especially one comprising one or more kingdoms) and ruled by a single supreme authority.
"the Russian empire"
2.nounA political unit ruled by an emperor or empress.
"The Empire of Vietnam was a short-lived client state of Japan governing Vietnam between March 11 and August 23, 1945."
3.nounA group of states or other territories that owe allegiance to a foreign power.
4.nounAn expansive and powerful enterprise under the control of one person or group.