a feather in his cap
Until modern times, ornamental feathers were more widely used by males than by females, and the nobility vied to find colorful and expensive plumage [(A lovely bird, the Norwegian blue: beautiful plumage)] to put on their hats. The military custom arose of using small feathers in lieu of badges of honor, and feathers, given to put in one’s cap, were awarded to those men who showed unusual gallantry. By the time the use of feathers had been abandoned, the phrase put a feather in one’s cap had already been integrated into the language, and so it continues to mean an honor or achievement.
-- Why You Say It, Webb Garrison

Five or six centuries ago, the expression was a literal statement; a man who had gained a distinction, especially on the battlefield, wore a feather in his cap as a token. In about the 15th century, any member of the English nobility was assumed to be a person of distinction, and feathers became a usual part of the headgear of nobility.
It is said that Edward the Black Prince, son of Edward III, won his spurs in the Battle of Crecy, at age 16, in 1346. He was awarded the crest of John, King of Bohemia, a French ally slain in battle. The crest consisted of three ostrich feathers, which then became the badge of the Prince of Wales and thence became a symbol of valorous deeds.
-- Hog on Ice & Other Curious Expressions, Charles Funk

to feather one’s nest
To provide for one’s comfort, especially for later life, by amassing wealth. The import is to the practice of many birds which, after building their nests, pluck down to provide a soft lining which will be comfortable during the long hours of incubation. The oldest English literary occurrence is in 1553, but a typical example from 1590 by poet Robert Greene was, “She sees thou hast fethred thy nest, and hast crowns in thy purse.”
-- Hog on Ice & Other Curious Expressions, Charles Funk

similarly,
-- Why You Say It, Webb Garrison

tarred and feathered
Subject to indignity and infamy. Once a literal punishment, in its severest form the victim was stripped and melted tar was poured or smeared on him and he was rolled in chicken feathers. The punishment was first inflicted in England in 1189 by Richard I for one guilty of theft in the Navy, but had been practiced in Europe in earlier years. In America, a royal officer was tarred and feathered in Boston in 1774, and other royalists received similar treatment by rebel mobs.
-- Heavens to Betsy! & Other Curious Sayings, Charles Funk

horsefeathers
Horsefeathers were rows of clapboards laid with the butt edges against the butt edges of shingles or clapboards so as to provide a flat surface over which asphalt or other shingles or siding could be laid; the term was in use in the building trade in New England and New York, at least through the 1950s. The term “feathering strips” was also used. “Horsefeathers” in the construction sense could be traced back at least to the 1900s, but its use to mean “nonsense” did not occur before 1925. ”It is my belief [says Charles Funk], therefore, that some bright chap heard the term used by an upstate builder, cleverly told the tale in a New York speakeasy of the period, and that “Horsefeathers!” was then picked up by doubting Thomases and used thereafter to greet any incredible statement.
-- Horsefeathers & Other Curious Words, Charles Funk

but:
Cartoonist Billy deBeck, creator of Barney Google, coined three slang expressions which have survived: heebie jeebies, hotsy totsy, and horsefeathers.
-- Who Put the Butter in Butterfly?, David Feldman