Definition of "Yen"

[...]Nothing but War was to be ſeen among ſo many different States, and their mutual Invaſions reduced the Empire into ſeven great Kingdoms, which were called Tſin, Tſou, Yen, Tchao, Han, Iſi, Ouei: The Kingdom of Yen, which at that time comprehended no more than the preſent Province of Petche li, made itſelf very ſoon Maſter of the Province of Leao tong, and by puſhing on its Conqueſts by degrees towards the Eaſt, Corea was at laſt brought under the Authority and wife Government of Tchen pen: This Kingdom for a long time withſtood the ambitious Attempts of the King of Tſin, called Tſin vang, but at laſt it fell under his Power as the other ſix had done: Hi vang, King of Yen and of Corea, was defeated, taken and killed in the Year 259 before the Birth of Chriſt, according to the Chineſe Hiſtory, and Tſin vang was acknowledged for Emperor of all China by the Name of Tſin chi hoang ti.

1739 , P. Du Halde, “Geographical Obſervations on the Kingdom of Corea”, in The General History Of China‎, 2nd edition, volume IV, page 388

9. Kingdom of Yen 燕Táking situated in lat. 39° 54' N., long. 116° 28' E., one of the districts of Shuntien fú in Chihlí, now occupies the site of the capital of the ancient kingdom of Yen, the most northern part of the empire under the reign of the Chau dynasty.

1849 August, “Annals of Confucius; or Chronology and Geography of the Chun Ts'iu”, in The Chinese Repository‎, volume XVIII, number 8, page 397

At that time, twenty-two centuries ago, a gentleman named Ching K'o was getting scandalously drunk in the market place of the capital of Yen, a feudal state in northwest China which owed nominal allegiance to the Son of Heaven (i.e., the emperor) though, in fact, there was no unified Chinese state.

1962, Leonard Cottrell, The Tiger of Chʻin: The Dramatic Emergence of China as a Nation‎, Holt Reinhart and Winston, pages 3–4

In 284 B.C., near the end of the Era of the Warring States, the state of Yen seized all but two of the more than 70 cities of the state of Ch'i. For five years, the loyal people of Ch'i defended those cities, namely, Chu and Chi-mo, against Yen's troops.

1965 May 1 , Kai-shek Chiang, “Documents: The President's Youth Day Message”, in Taiwan Today‎, archived from the original on 2023-05-30

The remaining major kingdoms (Han, Ch'u, Chao, Yen and Ch'i) searched for a means to stop the aggressive Ch'in, who appeared to have more in common witht he Hsiung-nu than with the Chinese.The solution seemed to appear in the kingdom of Yen with the arrival of Ching K’o in 237.

2001, George Fetherling, “CHING K'o”, in The Book of Assassins‎, Edison, NJ: Castle Books, published 2006, page 98

Numbering among those that comprised a virtual defensive line along the 42nd degree of latitude, where the state of Yen would construct its border wall in the Warring States period, it dates to the late Shang or very early Chou and typifies settlements that fully exploit riverside locations and natural ravines while being oriented to open vistas.

2011, Ralph D. Sawyer, Ancient Chinese Warfare‎, Basic Books, page 46