rotten to the core

rotten to the core idiom
Thoroughly bad, as in It seems that this police unit is rotten to the core, involved in numerous extortion schemes. The noun core here denotes the central part or heart of anything or anyone. The idiom was first recorded in 1804.

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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