Lily-livered

Meaning lacking in courage or cowardly was coined by Shakespeare in Macbeth (1605) Act V, Scene III, Macbeth says to a servant boy, “Thou lily-liver’d boy,” accusing him of cowardice. Ever since medieval times, the liver was thought to be the seat of all emotions, especially courage. Anything white or pale, like a lily, was thought to signify weakness, frailty or surrender. That is why flags of truce or surrender are white.