Chéng xīn literally means 'sincere heart'—combining 诚 (chéng), meaning 'honest,' 'genuine,' or 'sincere,' and 心 (xīn), meaning 'heart' or 'mind.' Together, they form a noun expressing authentic intent, heartfelt sincerity, or earnestness in attitude or action. It emphasizes inner truthfulness rather than outward appearance, often implying moral integrity and deep personal commitment.

This word is commonly used in contexts involving promises, apologies, efforts, or spiritual practice—for example, when someone makes a vow with full dedication or offers an apology from the bottom of their heart. While it can appear as a subject or object in sentences, it’s frequently modified by adjectives like 真诚的 (zhēnchéng de) or adverbs like 诚心诚意地 (chéngxīn chéngyì de). It carries a warm, respectful tone and is appropriate in both spoken and written Chinese, especially in formal or emotionally meaningful situations.