沆瀣一气 — “To collude with each other for sinister purposes”

During the Sui and Tang dynasties, scholars aspiring to become officials had to pass the imperial examination. During the reign of Emperor Xizong of Tang, a grand examination was held in the capital, Chang'an. Scholars from various regions, having already met certain qualifications, gathered in Chang'an to participate.

Among the many candidates, there was a talented scholar named Cui Xie. After completing his paper, he felt confident about his performance and eagerly awaited the results.

The official presiding over this examination was Cui Hang. As he reviewed Cui Xie's paper, he was increasingly impressed by its quality and decided to admit him. On the day the results were announced, Cui Xie was overjoyed to find his name on the successful candidates' list.

According to the customs of that era, those who passed the imperial examination were considered disciples of the chief examiner, who in turn was regarded as their patron and respectfully referred to as 'mentor' or 'benevolent teacher'. After the announcement, the newly successful scholars would pay a visit to their mentor. Cui Xie, of course, was no exception.

Cui Hang, as the patron, was particularly delighted to meet Cui Xie, a new disciple who happened to share his surname. It was a remarkable coincidence that the two characters 'Hang' ( ) and 'Xie' ( ) together form a compound word signifying night vapors, mist, or dew. Seizing upon this clever wordplay, people combined these two characters into a phrase: 'The patron and disciple, (hàng xiè yī qì).' This phrase metaphorically suggested that the teacher and student were intimately connected, much like the night vapors and dew.