median lethal dose

WordReference Random House Unabridged Dictionary of American English © 2025

me′dian le′thal dose′, 

1. Ecology, Drugs the quantity of a lethal substance, as a poison or pathogen, or of ionizing radiation that will kill 50 percent of the organisms subjected to it in a specified time period. Symbol: LD₅₀

• 1945–50

Collins Concise English Dictionary © HarperCollins Publishers::

median lethal dose, mean lethal dose noun

1. the amount of a drug or other substance that, when administered to a group of experimental animals, will kill 50 per cent of the group in a specified time
2. the amount of ionizing radiation that will kill 50 per cent of a population in a specified time

Abbreviation: LD₅₀