If you describe an achievement as a feather in someone's cap, you mean that they have done very well and people will admire them. It was a definite feather in his cap to have attended such a famous university. Hauptmann's arrest is a feather in the cap of the New Jersey police. Note: Traditionally, Native American warriors added feathers to their headdresses as a sign of bravery in battle. Medieval knights in England also wore feathers in their helmets as a sign of their bravery.