贺信
hèxìn · HSK 7
Congratulate
🎉✉️ 贺 = congratulate + 信 = letter, so a congratulation letter
贺 carries the sense of offering congratulations and 信 means letter or message. Together 贺信 is a written note of congratulations. The pronunciation hèxìn pairs hè (congratulate) with xìn (the same xìn as in 信件, mail).
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.