lethal

Lethal is an adjective describing something that causes death or is capable of causing death. It is used across many fields, including toxicology, medicine, genetics, law, and everyday language, to characterize agents, events, or conditions with the potential to result in fatal outcomes.

Etymology and usage notes: The word derives from Latin letalis, meaning deadly, from letum, death. In English, lethal has been used since the early modern period to distinguish death-causing properties from nonlethal effects. The related noun lethality denotes the capacity to cause death and is common in scientific and medical contexts.

Scientific and medical usage: In toxicology and pharmacology, lethal dose and lethal concentration concepts quantify potency. LD50 refers to the dose required to kill 50% of a test population, while LC50 denotes the concentration in air or water that kills 50%. These measures are highly dependent on species, exposure route, and biological factors. Lethality is a central concept in risk assessment, drug development, and safety regulation.

Biology and genetics: In genetics, a lethal allele can cause death when present in certain genotypes, often during embryonic development. Embryonic lethality and postnatal lethality describe death occurring before birth or after birth, respectively. Researchers study lethal mutations to understand developmental pathways and essential biological functions, sometimes using conditional or stage-specific lethality to probe gene roles.

Law, ethics, and society: The term also appears in the context of lethal force, which is force capable of causing death and is regulated by legal frameworks to balance safety and rights. Lethal weapons, injections, and other fatal applications raise ethical, legal, and policy considerations.

See also: lethality, toxicity, fatality, dosage.