致 means 'to cause' or 'to bring about', and 命 means 'life' or 'destiny'. Together, 致命 literally means 'life-causing' — that is, causing the end of life. It functions almost exclusively as an adjective describing something that causes death or has deadly consequences, such as a disease, injury, weapon, or error. It carries strong, formal weight and is common in medical, legal, journalistic, and technical contexts.

Unlike more colloquial terms like 要命 (yào mìng, 'terrible' or 'exhausting'), 致命 is serious and precise — it implies actual, irreversible fatality, not exaggeration. It often modifies nouns directly (e.g., 致命伤 'fatal wound') or appears after 是 in descriptive clauses (e.g., 这种病毒是致命的). It is rarely used predicatively without 的 in spoken Chinese, and never in casual or humorous contexts.