From Longman Dictionary of Contemporary Englishbe kingbe kingPOPULARif something is king at a particular time, it has a big influence on people back in the days when jazz was king → king
Examples from the Corpus
be king• The new king, I suppose, if you can be king without a land.• In the arts, too, contention is king.• In Ephyre, the city later called Corinth, Glaucus was King.• During the middle 1800s, cotton production was king in the South.• As at the weight-loss programs I attended in junior high, the scale was king here.• In 1995, it was stock -- not cash -- that was king.• He was born to be King and was looking for a princess.• If the flounder still exists it will be king. - foreign words and phrases scattered here and there! 