Deadly

Deadly is an adjective used to describe something that can cause death or is capable of causing death. It is applied to physical agents such as a deadly poison or deadly toxin, diseases with high mortality, or weapons and means of harm. The term also functions as a figurative intensifier in informal speech, as in a deadly serious situation or a deadly accurate shot.

Etymology and related terms: The word derives from the adjective dead with the suffix -ly. In older English, it meant “causing death” and over time broadened to include strong or extreme qualities. In technical contexts, terms like lethality and lethal are closely related and used to describe the capacity to cause death.

Context and usage: In medicine and public health, "deadly" describes agents with the capacity to kill, such as certain pathogens or toxins, or the fatality of a disease. In law and public safety, "deadly weapon" refers to items capable of causing deadly injury, with definitions varying by jurisdiction. In everyday language, "deadly" also conveys intensity or danger, as in phrases like "deadly serious" or "deadly quiet." Because of its strong meaning, the word can carry emotional weight and may be considered alarming in some contexts. See also lethality, lethal, mortality.