无效 (wú xiào) is an adjective meaning 'ineffective' or 'ineffectual'—describing something that fails to produce the intended result. The character 无 means 'without' or 'not,' and 效 means 'effect,' 'result,' or 'efficacy.' Together, they literally mean 'without effect,' capturing the idea of failure to achieve a purpose. It’s commonly used in formal, technical, or administrative contexts—especially in medicine, law, and technology—to describe treatments, agreements, actions, or systems that lack desired outcomes.

This word often appears in written Chinese more than in casual speech. It carries a neutral-to-negative connotation and implies objective failure rather than subjective disappointment. You’ll frequently see it in phrases like '治疗无效' (treatment ineffective), '合同无效' (contract void/invalid), or '措施无效' (measures ineffective). Unlike colloquial alternatives such as '不管用' (guǎn bù yòng), 无效 is precise, concise, and widely understood across domains requiring clarity about functional failure.