{n. phr.} Something to be proud of; an honor. * /It was a feather in his cap to win first prize./ (From the medieval practice of placing a feather in the helmet of one who won honors in battle.)
FEATHER IN ONE'S CAP
Meaning of FEATHER IN ONE'S CAP in English
Slang English vocab. Английский сленговый словарь. 2012