king W1 [countable]
a man who rules a country because he is from a royal family [↪ queen]
Henry VIII, King of England
On 2 December Henry VI was crowned king (=made the king at an official ceremony).
someone or something that people think is the most important or best of a particular type of person or thing:
the King of Rock 'n' Roll
the king of Swiss cheeses
The lion is the king of the jungle.
if you live like a king, feel like a king etc, you are very successful, happy, rich etc:
With her at my side, I felt like a king.
the most important piece in chess
a playing card with a picture of a king on it
if something is king at a particular time, it has a big influence on people:
back in the days when jazz was king
a very large amount of money