仔細 (zǐ xì) is an adjective meaning 'careful' or 'meticulous', describing someone who pays close attention to detail and avoids mistakes through thoroughness. The character 仔 originally meant 'young animal' but in this compound it contributes a sense of smallness or attentiveness; 細 means 'fine', 'thin', or 'detailed', reinforcing the idea of precision. Together, they form a vivid image of examining something closely, like inspecting fine threads.

This word is commonly used to describe behavior, work habits, reading, listening, or observation — for example, reading instructions carefully before assembling furniture, or checking calculations twice. It often appears in imperative contexts ('Be careful!') or descriptive ones ('a meticulous researcher'). While it can function adverbially in informal speech (e.g., 仔細看), its core grammatical role is adjectival and it typically modifies nouns or follows verbs like 是 or 很.