walking encyclopedia
A very knowledgeable person, as in Ask Rob—he's a walking encyclopedia of military history. A similar expression, a walking dictionary, was used by George Chapman in his poem “Tears of Peace” (c. 1600).
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The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.