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Webster 1913 Edition

Noun.

[Cf. G.

knopper

. See

(Zool.)

A kind of gall produced by a gallfly on the cup of an acorn, – used in tanning and dyeing.

knoppern ‎(plural knopperns)

A kind of gall produced by a gallfly on the cup of an acorn, and formerly used in tanning and dyeing.