Why is a Cowardly Person Called “Yellow” and Where Did the Expression Come From?

Yellow, meaning cowardly, is actually an abbreviation of yellow dog, an American insult that first appeared in the nineteenth century to describe a cowardly or worthless person.

In the early twentieth century, when employers were fighting trade unions, they insisted that new employees sign a pledge never to join a union.

This pledge was called a “yellow dog” contract by union members with the implication that anyone signing it was “yellow.”