From Longman Dictionary of Contemporary Englishdefoliantde‧fo‧li‧ant /diːˈfəʊliənt $ -ˈfoʊ-/ noun [countable, uncountable] formal HBPa chemical substance, used especially in war, that makes all the leaves of plants drop off
Examples from the Corpus
defoliant• Chemical defoliants would not be used against crops, nor would producers be arrested or property confiscated.Origin defoliant (1900-2000) Medieval Latin defoliare, from Latin folium “leaf” 