(?427-347BC) an ancient Greek philosopher, who had a very great influence on European philosophy. He explained his ideas in the form of written conversations. His teacher was Socrates, and after Socrates' death he established a school called the Academy, where Aristotle was one of his students. His most famous work is The Republic, about the perfect state and form of government.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.