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Webster 1913 Edition

Noun.

One who, or that which, gnaws.

(Zool.)

A rodent.

Noun.

naw'er. He or that which gnaws or corrodes.

gnawer ‎(plural gnawers)

A rodent or other similar type of animal that gnaws.
- 1839, Charles Darwin, The Voyage of the Beagle, Chapter 7,
  South America is characterized by possessing many peculiar gnawers […] .
- 1947, Lloyd Glenn Ingles, Mammals of California, Stanford University Press, p. 182,
  The Norway Rat is a good digger and a superb gnawer.

rodent or other similar type of animal that gnaws