(1921-89) a Russian physicist who helped to develop the Soviet hydrogen bomb and who was also a dissident (=someone who criticizes his country's government and is badly treated because of his beliefs). He won the Nobel Peace Prize in 1975, but the Soviet government would not allow him to travel to Norway to receive it. He was sent away from Moscow as a punishment, until MikhailGorbachev became Soviet president and allowed him to return.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.
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