feather in one’s cap, a

A special honor or achievement. This term comes from the custom of numerous peoples—American Indian tribes, Turks, Himalayan peoples, among others—of placing a feather in a soldier’s cap for every enemy he kills. The term began to be used figuratively by the early seventeenth century and was a cliché by the time Laurence Sterne wrote, “The feather put into his cap of having been abroad” (Tristram Shandy, 1761–67).