坚信
jiān xìn · HSK 7
to believe firmly
🪨 坚 firm/solid + 信 trust = trust that stays solid: to believe firmly
坚 also shows up in 坚强 (strong) and 坚持 (persist) — it tags things that hold firm. 信 is the trust/belief in 信任 and 相信. Stack them and the belief is rock-solid, held without any doubt.
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.