knopper gall
/ˈnɒpə(r)/noun
1- a hard, irregular umbrella-like gall which forms on an oak acorn in response to the developing larva of a gall wasp（橡实对瘿蜂幼虫成长起反应而形成的）瘿。
1.1
- The wasp is Andricus quercuscalicis, family Cynipidae.栎萼瘿蜂（拉丁名Andricus quercuscalicis）属于瘿蜂科。
词源
late 19th cent.: knopper from German Knopper 'gallnut'.