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yellow streak

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noun Informal.
  1. a trait of cowardice in a person's character.

Origin of yellow streak

An Americanism dating back to 1910–15
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for yellow streak

yellow streak

noun
  1. informal a cowardly or weak trait, characteristic, or flaw in a person's nature
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012