tomatillo UK /ˌtɒm.əˈtiː.(j)əʊ/US /ˌtoʊ.məˈti.(j)oʊ/ noun1 •A plant of the nightshade family originating in Mexico, Physalis philadelphica, cultivated for its tomato-like green to green-purple fruit surrounded by a thin papery skin. formstomatilloes · tomatillos