Where does the word tycoon come from?

Tycoon is usually translated into English as "great lord". The word is derived from the Japanese word taikun (大君?).  In English tycoon it has an additional pejorative connotations, suggesting an excessive exercise of power and wealth. 

Origin

Tycoon entered the English language in 1857 after the 'opening of Japan' by Commodore Perry, symbolised by the Treaty of Kanagawa in 1854. 

The term spread to the business community, where it has been used ever since. Source