de ‧ fo ‧ li ‧ ant /diːˈfəʊliənt $ -ˈfoʊ-/ BrE AmE noun [uncountable and countable] formal
[ Date: 1900-2000 ; Language: Medieval Latin ; Origin: defoliare , from Latin folium 'leaf' ]
a chemical substance, used especially in war, that makes all the leaves of plants drop off