可信
kě xìn · HSK 7
trustworthy
🤝 可信 = 可 (can / -able) + 信 (trust, believe): able-to-be-believed = trustworthy
可 marks something as possible or worthy of an action, and 信 is to trust or believe. Stick them together and you get worthy-of-belief. The same 可 shows up in 可爱 (loveable) and 可靠 (reliable).
可 — mouth 口 + breath marker 丁 (modified)
可 originally depicted a mouth (口) with a curved stroke suggesting exhaled breath or speech, conveying approval or assent. From this came the meaning 'to permit' or 'can,' as granting permission was expressed verbally. Today it broadly means 'may,' 'can,' or 'approve.'
信 — person 亻 + speech 言
信 combines 亻(person) with 言(speech), depicting a person standing by their words. The original sense is 'truthfulness' or 'sincerity'—what a person says can be trusted. From this it extended to 'believe,' 'trust,' and later 'message' or 'letter,' since a letter carries one's word.