Whether it's ancient times or modern days, trust and credibility are essential to the fabric of society. The Chinese character for "credibility" is 信 (xìn). Its form is rather self-explanatory: on the left is 亻, the "people" radical, and on the right is 言, meaning "words" – together, they suggest a person speaking honest words.

The original meaning of 信 is "honest" or "truthful". An early example was the idiom 信誓旦旦 (xìn shì dàn dàn), which means "to pledge or promise in all sincerity and seriousness". First used in the Classic of Poetry (《诗经》shī jīng), the idiom describes an abused woman recalling how her husband, after three years of marriage had vowed solemnly to love her before their wedding. Still in use today, this idiom is usually applied in the negative, with the connotation that such promises were not kept.

Pretty words are not always truthful; indeed, the truth can often be ugly, as stated in the saying from the classic Daoist text, Daodejing (《道德经》dào dé jīng): "信言不美，美言不信" (xìn yán bù měi, měi yán bù xìn; "truthful words are unpleasant, while pleasant words are not truthful").

Those who speak truthfully and always keep their promises are able to maintain credibility with their audience. Thus 信 later took on the meaning of "credibility." Keeping your promise is 守信 (shǒu xìn, "keep credibility"), while breaking faith is 失信 (shī xìn, "lose credibility"). When it comes to the importance of being honest and honorable, one can expect a lecture from the likes of Confucius, who offers wisdom such as "Always keep your promises among friends" (与朋友交，言而有信 yǔ péng yǒu jiāo, yán ér yǒu xìn), and "Promises must be kept, and action must be resolute" (言必信，行必果 yán bì xìn, xíng bì guǒ).

In modern days, we could hardly operate without 信用 (xìn yòng, credit, credibility), especially in the financial world: We have credit cards (信用卡 xìn yòng kǎ), credit unions (信用社 xìn yòng shè), credit loans (信贷 xìn dài), and trusts (信托 xìn tuō). Business has to be built on reputation and prestige, 信誉 (xìn yù).

Credibility engenders trust, therefore, 信 can also mean to "trust, believe," as in the verb 信任 (xìn rèn, "trust") and 相信 (xiāng xìn, "to believe"). Religious faith is 信仰 (xìn yǎng), while superstitions are 迷信 (mí xìn), which translates literally as "confused belief." On the other hand, confidence, which is to “believe in yourself”, is 自信 (zì xìn).

The character 信 can also be a token of trust, or serve as a credential. Letters are sometimes referred to as 信, because they carry trusted messages from one person to another (such as the confidential memos sent to emperors). Along this line, 信 can also refer to messages, news, and "information," which is 信息 (xìn xī).

Source：The World of Chinese