old-fashioned

a yellow-bellied person is not at all brave.

You're a load of yellow-bellied fools, too frightened to stand up for what you believe in!

• be on the side of the angels
• be on the skids
• be on the square
• be on the threshold of
• be on the threshold of doing something
• be on the threshold of something
• be on the tip of tongue
• be on the tip of your tongue
• be on the wagon
• be on the warpath
• be on the wing
• be on the wrong end of
• be on the wrong end of something
• be on the wrong side of
• be on the wrong track
• be on thin ice
• be on to a good thing
• be onto a winner
• be on top of the world
• be on uppers
• be on your best behaviour
• be on your guard
• be on your last legs
• be on your mettle
• be on your tail