feather in one's cap, a

feather in one's cap, a

An act or deed to one's credit; a distinctive achievement. For example, Getting all three factions to the bargaining table would be a feather in his cap. This expression alludes to the practice of putting a feather on a soldier's cap for every enemy he kills, an early practice of some Native American tribes and many other peoples. [Early 1600s]
See also: feather