When combined, 出卖 (chūmài) literally means “to sell out” or “to put out for sale.” This literal foundation makes its figurative meaning incredibly intuitive: you are “putting your loyalty out for sale” to the highest bidder. This is why the term so strongly implies that the betrayal was committed in exchange for some benefit.
In Chinese culture, where group harmony and collective identity are paramount, loyalty (忠诚, zhōngchéng) is a foundational virtue. This applies to family, friends, the workplace, and especially the nation. 出卖 (chūmài) is the ultimate violation of this virtue. It's not just a personal offense; it's an act that shatters relationships and threatens the integrity of the group. A concept that helps understand the gravity of 出卖 is 义气 (yìqì), often translated as “code of brotherhood,” “honor,” or “righteousness.” It's the unspoken rule of unwavering loyalty and support among friends or sworn brothers, a major theme in Chinese literature like Romance of the Three Kingdoms and countless martial arts films. To 出卖 a friend who you share 义气 with is one of the most despicable acts a person can commit. Compared to the English word “betray,” 出卖 (chūmài) often feels more transactional and severe. While you can “betray” a secret by accidentally letting it slip, 出卖 implies a conscious, deliberate act of trading that secret for a reward. It's closer in feeling to the English phrase “to sell someone down the river,” which captures the sense of treachery for personal gain.
出卖 is a strong word. You wouldn't use it for minor disagreements. It's reserved for serious breaches of trust.