A brown rat.Licensed from iStockPhoto
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
a common, omnivorous large rat (Rattus norvegicus) that swims and dives well, usually lives in underground burrows, and spreads various diseases: the mutant form, a white rat, is used for medical experiments
Used by arrangement with John Wiley & Sons, Inc.
nounThe American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
See Norway rat.