What does lethal mean?
Lethal means capable of causing death, and it is frequently used in reference to doses, weapons, forces, diseases, and other things whose effects can be fatal. The adjective is especially familiar in medical, legal, military, and public-safety contexts, as in “lethal dose,” “lethal force,” and “lethal weapon.” It can also be used more figuratively for a strategy, condition, or development that is devastating to a person, organization, or system. Lethal is often somewhat more formal than deadly, while fatal tends to place greater emphasis on an outcome that leads to death rather than merely on the capacity to cause it. The word’s history traces directly to Latin, where lethalis meant “deadly” and was derived from letum, the Latin word for death. Learning the word therefore also connects its precise meaning with its unmistakable Roman origin.
adjectiveCapable of causing death; deadly. It can also describe something profoundly harmful or destructive.
- Capable of causing death.
- So harmful, destructive, or disruptive as to be potentially fatal.
"The scientist warned that even a small dose of the toxin could be lethal."
"Emergency crews isolated the area after finding a lethal quantity of the chemical."
"The company introduced a new pricing strategy that proved lethal to its smaller competitors."
Lethal carries a Roman fingerprint: it comes from the Latin letum, the word for death.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does lethal come from?
Lethal entered English in the early 17th century from Latin lethalis, meaning “deadly” or “causing death.” Latin lethalis was derived from letum, meaning “death.” The uncommon English adjective letal is a direct cognate sharing this Latin origin.
Related word forms
How lethal is actually used
Lethal is especially common in medical, legal, military, and safety contexts. It is generally more formal than deadly and often focuses on the capacity to cause death or catastrophic harm.
Easily confused with lethal
Fatal typically emphasizes that something leads to death, whereas lethal describes something capable of causing death, such as a dose, weapon, or force.