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.
One of the light, flat structures that cover the skin of birds. A feather is made of a horny substance and has a narrow, hollow shaft bearing flat vanes formed of many parallel barbs. The barbs of outer feathers are formed of even smaller structures (called barbules) that interlock. The barbs of down feathers do not interlock. Evolutionarily, feathers are modified scales, first seen in certain dinosaurs.
To be primarily concerned with one's own gain; take care of oneself (1590+)