LETHAL (Lat. lethalis, for letalis, deadly, from letum, death; the spelling is due to a confusion with Gr. X^TJ, forgetfulness), an adjective meaning " deadly," " fatal," especially as applied to weapons, drugs, etc. A " lethal chamber " is a room or receptacle in which animals may be put to death painlessly, by the admission of poisonous gases.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)