1. Causing or capable of causing death.
2. Causing ruin or destruction; disastrous: "Such doctrines, if true, would be absolutely fatal to my theory" (Charles Darwin).
3. Of decisive importance; fateful: came through at the fatal moment.
4. Concerning or determining one's fate: the fatal thread of life.
5. Obsolete Having been destined; fated.
[Middle English, fateful, from Old French, from Latin fātālis, from fātum, prophecy, doom; see FATE.]
Synonyms: fatal, deadly, lethal, mortal
These adjectives apply to what causes or is likely to cause death. Fatal describes conditions, circumstances, or events that have already caused death or are virtually certain to do so in the future: a fatal accident; a fatal illness.
Deadly means capable of killing or of being used to kill: a deadly poison; a deadly weapon.
Lethal has a similar range, often with a suggestion of deliberate or calculated intent: execution by lethal injection; the lethal technology of modern warfare.
Mortal describes a condition or action that produces death, typically in a context of combat: a mortal wound; delivered a mortal blow.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.