Entry from British & World English dictionary
Definition of knopper gall in English:
A hard, irregular umbrella-like gall which forms on an oak acorn in response to the developing larva of a gall wasp.
- The wasp is Andricus quercuscalicis, family Cynipidae
late 19th century: knopper from German Knopper 'gall'.
Definition of knopper gall in: