The Japanese word Taikun means 'great lord.' Commodore Perry brought the word to the United States in 1857 when he returned from his travels. It gained popularity in the United States when two aides of Abraham Lincoln, John Nicolae and John Hay, took to calling Lincoln a tycoon as a joke. It would later spread to use in the business world, which soon became its normal usage.
A tycoon is generally someone well known in the business world who has dominated an area of business. They are powerful and have great wealth. Other words to describe a tycoon might be a magnate, czar, mogul, baron, or oligarch. It generally implies a great deal of power.
Some tycoons throughout history have been oil tycoon John D. Rockefeller, whose company was Standard Oil, steel tycoon Andrew Carnegie, and automobile tycoon Henry Ford. It was a very popular term in the 29th and 20th centuries. Who would you consider to be modern-day tycoons?