a yellow streak

yellow streak

A tendency to be cowardly or easily frightened. She likes to strut around like she's the boss of the place, but she has a yellow streak running down her spine if you ever confront her on an issue. He knew what they were doing was wrong, but his yellow streak kept him from intervening.
See also: streak, yellow
Farlex Dictionary of Idioms.

a ˈyellow streak

(disapproving) the quality of being easily frightened; cowardice: He won’t fight? I always thought he had a yellow streak in him.
Yellow is often used to describe somebody who is a coward.
See also: streak, yellow
Farlex Partner Idioms Dictionary
See also:
  • appear to
  • a change of heart
  • a tough cookie
  • a tough customer/cookie
  • a mystery to (one)
  • a turn of phrase
  • able to do
  • able to do it
  • a shoulder to cry on
  • a piece of the action
References in periodicals archive
I have often being accused of having a yellow streak running down my back - not that anyone has been brave enough to say it to my face.
Queen keeps it light; RESULT!
In America, it can evoke cowardice (a yellow streak) or faithfulness (a yellow ribbon).
Global communication comes into its own