确信
què xìn · HSK 7
to be sure
✅ 确 = certain + 信 = believe; to be certain in your belief, i.e. convinced
确 carries the sense of solid or true, and 信 means to trust or believe. Stacked together they mean a belief held as solid fact: to be sure, positive, firmly convinced that something is so.
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.