1. any plant louse of the family Aphididae, characterized by a waxy secretion that appears like a jumbled mass of fine, curly, white cottony or woolly threads, as Eriosoma lanigerum (woolly apple aphid or American blight) and Prociphilus tessellatus (woolly alder aphid) .
2. any of various aphids that produce white waxy threads, as Adelges piceae (balsam woolly aphid) .
[ 1835-45 ]