执牛耳

Traditional (Taiwan): 執牛耳

zhíniú'ěr ㄓˊ ㄋㄧㄡˊ ㄦˇ

    • to be the acknowledged leader (from the custom of a prince holding a plate on which lay the severed ears of a sacrificial bull at an alliance ceremony)

Character by character

Saying俗语俗語

Idiom惯用语 · Widely known

Literally
hold the ox's ear
Meaning
To be the leader in some field. In ancient times the leader of an alliance held the ox's ear to take its blood when the lords swore an oath.

Sources