東道主

Etymology
Attested in , in the entry for the 30th year of Duke Xi's reign (《左傳·僖公三十年》):

Uttered by Zhu Zhiwu (燭之武), a Zheng courtier, during his negotiation with the Count Mu of Qin (秦穆公) who was laying siege to the state of Zheng. Later used idiomatically as a generic term for a host.

Noun

 * 1) host

Usage notes
Some dictionaries classify as a chengyu, albeit a three-character one.