Feather in one’s cap
A feather in one’s cap signifies a laudatory achievement. The expression has been used in this figurative sense since the 18th century. The wearing of feathers in headdress to mark bravery or distinction goes back to antiquity in many cultures around the world. It was common practice in Europe during The Middle Ages. Edward the Black Prince (1330-1376) so called because of his black armour, wore three ostrich plumes in his helmet, which then became the royal crest of Princes of Wales ever since.