万乘

In the Zhou system, only the Son of Heaven could field ten thousand 乘 (four-horse war chariots), so 万乘 became a metonym for 'the emperor' or 'the imperial position'. Compare 千乘之国 — a thousand-chariot state, a major feudal power but rank below the emperor.

usage

The 乘 is the classical military-chariot reading shèng, not the everyday chéng. Purely literary today — encountered only in classical Chinese or historical writing.