Old English feðer "a feather; a pen," in plural, "wings," from Proto-Germanic *fethro (source also of Old Saxon fethara, Old Norse fioþr, Swedish fjäder, Middle Dutch vedere, Dutch veder, Old High German fedara, German Feder), from PIE *pet-ra-, from root *pet- "to rush, to fly."
Feather-headed "silly" is from 1640s. Feather-duster attested by 1835. Figurative use of feather in (one's) cap attested by 1734. Birds of a feather "creatures of the same kind" is from 1580s; the same image is in Greek homopteros (variant birds of a beak is from c. 1600).