Definition of lethal in English:

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Pronunciation: /ˈlēTHəl/


1Sufficient to cause death: a lethal cocktail of alcohol and pills
More example sentences
  • In sufficient quantities its spores can be lethal to humans.
  • Grey squirrels have out-competed reds for food and also carry squirrel-pox virus which is lethal to the native animals.
  • The gas acts like mustard gas, and can prove lethal to those with respiratory problems.
1.1Harmful or destructive: the Krakatoa eruption was the most lethal on record
More example sentences
  • Friday was a bizarre affair, fuelled by a lethal combination of beer, wine, Jack Daniels and vodka.
  • The cider and vodka combination is far too lethal for my poor liver so I ended up puking.
  • Entire governments, never mind single ministers, have been toppled by that lethal combination.
dangerous, destructive, harmful, pernicious
literary deathly, nocuous


Late 16th century (in the sense 'causing spiritual death'): from Latin lethalis, from lethum, a variant (influenced by Greek lēthē 'forgetfulness') of letum 'death'.

  • When the souls of the dead in Greek mythology drank the water of Lethe, a river in Hades, the underworld, they forgot their life on earth, and so in Greek the word Lēthē meant ‘forgetfulness’. Many ancient Romans were familiar with this, and along the line they altered their Latin word letum ‘death’ to lethum, to be closer to the Greek. The altered Latin form is the source of English lethal ‘deadly’. Lethargy (Late Middle English) comes from a related Greek word.

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Syllabification: le·thal

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