小偷 (xiǎo tōu) literally means 'small thief' — 小 (xiǎo) means 'small' or 'little', and 偷 (tōu) means 'to steal'. Though the characters suggest a diminutive form, the term is not childish or endearing; instead, it’s the most common colloquial word for 'thief' in everyday Mandarin. It carries a neutral-to-slightly-negative tone and is widely used in speech and informal writing — for example, in news headlines, casual warnings, or storytelling. Unlike formal terms like 窃贼 (qiè zéi), 小偷 is accessible and frequently heard in daily conversation.

The word usually refers to someone who commits petty theft — such as shoplifting or pickpocketing — rather than major crimes like robbery or burglary. It can be used alone or with modifiers (e.g., 捕获小偷 'arrest the thief', 可疑的小偷 'a suspicious thief'). While grammatically a noun, it rarely takes aspect markers (like 了 or 过) directly — those attach to the verb 偷 instead (e.g., 他偷了钱包, not 他小偷了钱包).