Imperialism is a system or policy of controlling other countries or territories by a rich and powerful country or empire. Learn the meaning , synonyms, sentences, and word origin of imperialism from Collins English Dictionary. Imperialism definition : the policy of extending the rule or authority of an empire or nation over foreign countries, or of acquiring and holding colonies and dependencies.. See examples of IMPERIALISM used in a sentence. What is Imperialism ? According to definition of John A. Hobson, “ Imperialism is the policy of extending the control or authority of a state over foreign countries and of acquiring and holding colonies and dependencies.” Simply the meaning of Imperialism is the policy or practice by which a powerful nation extends its control over other countries or territories, often through military conquest, political dominance, or economic exploitation, to expand its power and influence. It typically ... Definition of imperialism noun in Oxford Advanced Learner's Dictionary. Meaning , pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.