Old English feðer "feather," in plural, "wings," from Proto-Germanic *fethro (cf. 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" (see petition (n.)). Feather-headed "silly" is from 1640s. Feather duster attested by 1858. Figurative use of feather in (one's) cap attested by 1734.
Old English fiðerian "to furnish with feathers or wings," from feðer (see feather (n.)). Meaning "to fit (an arrow) with feathers" is from early 13c.; that of "to deck, adorn, or provide with plumage" is from late 15c. In reference to oars (later paddles, propellers, etc.) from 1740. Phrase feather one's nest "enrich oneself" is from 1580s. Related: Feathered; feathering.
In good form or well-dressed; also, in excellent spirits or condition: in fine feather today