坚信 means 'to firmly believe' — a strong, unwavering conviction that something is true or will happen. The first character 坚 (jiān) means 'firm', 'solid', or 'resolute', often implying endurance or steadfastness; the second character 信 (xìn) means 'to believe' or 'trust'. Together, they form a compound verb emphasizing deep confidence, not just casual belief. It’s commonly used in formal writing, speeches, personal reflections, and discussions about values, goals, or principles.

This word conveys emotional certainty and moral commitment — for example, believing in justice, one’s abilities, or scientific facts. Unlike simpler verbs like 相信 (to believe), 坚信 implies persistence despite doubt or opposition. It’s typically followed by a clause introduced by that (that something is true), or a noun phrase (e.g., 坚信真理 — 'firmly believe in truth'). It rarely appears in casual spoken Chinese and is more common in written or elevated spoken contexts.