Informal One that is exceptionally, often excessively industrious or zealous: "The eager beavers of industry seldom reach their potential, much less rise to the top” ( Newsweek). (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.