noun
An organophosphate insecticide used in agriculture and public health. The name is a katakana rendering of the chemical name plus 剤 (agent).
See also: マラチオン
マラソン剤は、蚊の駆除に使われることがある。
Malathion is sometimes used for mosquito control.
マラチオン is the direct katakana transcription of malathion, while マラソン剤 explicitly adds 剤 to indicate it is a formulated product.
From English malathion, with the suffix 剤 (zai, 'agent, preparation') added to form a compound noun.