'偷偷' is an adverb formed by reduplicating the verb 偷 (tōu), meaning 'to steal'. Though its literal origin relates to stealing, in modern usage it almost never implies actual theft. Instead, it conveys the idea of doing something quietly, secretly, or without others noticing — often with a hint of playfulness, shyness, or mild guilt. It emphasizes the manner of action: discreetly and covertly.

This word commonly modifies verbs and appears before them in sentences (e.g., 偷偷看, 偷偷吃). It’s frequently used in everyday contexts like eating snacks without permission, glancing at someone when you think they’re not looking, or slipping away unnoticed. It carries a soft, colloquial tone — appropriate in informal speech and writing but avoided in formal reports or official documents. While the characters are identical, the repetition creates a distinct grammatical function: reduplication here shifts the word from verb to adverb, a common pattern in Chinese for expressing manner or attenuation.