丝毫无损 literally means 'not even a thread or a hair harmed' — combining 丝 (thread) and 毫 (a tiny hair), both symbolizing the smallest possible measure, with 无 (without) and 损 (damage). Together, they emphasize absolute absence of harm or injury. This phrase is highly idiomatic and formal, often used in written Chinese or serious spoken contexts to stress complete physical or functional integrity after a potentially dangerous event.

It commonly appears in news reports, medical summaries, safety assessments, or descriptions of objects surviving accidents — for example, after an earthquake, fire, or collision. Though it describes a state (like an adjective), it functions predicatively (e.g., 'X is 丝毫无损') and rarely appears attributively before a noun without additional structure (e.g., '丝毫无损的状态'). It conveys relief or reassurance, carrying a tone of precision and gravity.