from The Century Dictionary.
- noun A kind of gall formed from the immature acorns of Quercus pedunculata and Q. sessilifolia, abounding in Croatia, Styria, etc. These galls are largely used for tanning throughout Austria, and to some extent in Germany. They are also used in dyeing. Also
Sorry, no etymologies found.
The knopper is generally found on the acorn or leaf of the oak tree.