noun
lethal dose; fatal dose
The amount of a substance (drug, poison, radiation, etc.) that causes death. Often used in medical, toxicological, and forensic contexts.
この薬の致死量は体重1キログラムあたり10ミリグラムです。
The lethal dose of this drug is 10 milligrams per kilogram of body weight.
致死量の放射線を浴びると数週間以内に死亡する。
Exposure to a lethal dose of radiation causes death within a few weeks.
中毒量 means 'toxic dose' (causing poisoning but not necessarily death), while 致死量 specifically means a dose that causes death.
Compound of 致死 (ちし, 'lethal, fatal') and 量 (りょう, 'amount, dose'). The word is a straightforward Sino-Japanese technical term.