a yellowish or colorless, acrid liquid, CH:CHCHO, whose fumes irritate the eyes: it is formed by the decomposition of glycerol and is used in organic synthesis and in plastics, poison gas, etc.
See acrolein in American Heritage Dictionary 4
(ə-krōˈlē-ĭn)
noun
A colorless, flammable, poisonous liquid aldehyde, CH2CHCHO, having an acrid odor and vapors irritating to the eyes.