十分 (shí fēn) is an adverb meaning 'very' or 'extremely', used to intensify adjectives, verbs, or other adverbs. Literally, 十 means 'ten' and 分 means 'part' or 'portion', so together they evoke the idea of 'ten parts out of ten' — i.e., full measure or completeness. This etymology explains why 十分 conveys maximum degree, similar to English expressions like '100%'. It’s more formal and literary than colloquial intensifiers like 很 or 特别, and commonly appears in written Chinese, speeches, and polite conversation.

十分 is typically placed directly before the word it modifies — for example, 十分高兴 (very happy), 十分重要 (extremely important), or 十分感谢 (deeply grateful). Unlike some intensifiers, it cannot stand alone as a response and must always modify another element. It’s frequently used in positive evaluations, expressions of gratitude, or emphasis on quality or degree, especially when conveying sincerity or seriousness.