an insect in the family Cynipidae (cynipid wasps) or Eurytomidae (eurytomids), whose larvae cause many kinds of galls on trees, particularly oaks —note 1. e.g., the oak apple galls, gouty oak galls, and horned oak galls are caused by cynipid wasps; Euura sawflies in the family Tenthredinidae also produce galls on willow —note 2. true wasps are in the family Vespidae This definition last updated 10/24/2008