feath·er 
(fĕthər)
(fĕthər)n.
1. One of the light, flat structures growing from the skin of birds, consisting of numerous slender, closely arranged parallel barbs forming a vane on either side of a horny, tapering, partly hollow shaft.
2. A feathery tuft or fringe of hair, as on the legs or tail of some dogs.
3. Character, kind, or nature: Birds of a feather flock together.
4.
a. A strip, wedge, or flange used as a strengthening part.
b. A wedge or key that fits into a groove to make a joint.
5. The vane of an arrow.
6. A feather-shaped flaw, as in a precious stone.
7. The wake made by a submarine's periscope.
8. The act of feathering the blade of an oar in rowing.
v. feath·ered, feath·er·ing, feath·ers
v. tr.
1. To cover, dress, or decorate with feathers or featherlike projections.
2. To fit (an arrow) with a feather.
3.
a. To thin, reduce, or fringe the edge of (wood, for example) by cutting, shaving, or making thinner.
b. To spread (paint, for example) thinly at the edges so as to blend with the surrounding area.
c. To shorten and taper (hair) by cutting and thinning.
d. To blur or soften the edge of (an image).
4. To apply (a brake, throttle, or other control) gently or slightly and steadily.
5. To turn (an oar blade) almost horizontal as it is carried back after each stroke.
6.
a. To alter the pitch of (a propeller) so that the chords of the blades are parallel with the line of flight.
b. To alter the pitch of (the rotor of a helicopter) while in forward flight.
7. To turn off (an aircraft engine) while in flight.
v. intr.
Idioms: 1. To grow feathers or become feathered.
2. To move, spread, or grow in a manner suggestive of feathers: “Steam feathered out from under the bathroom door” (Melinda Hayes).
3. To become thin or less dense at the edges: “That lipstick had feathered out in the corners of her mouth” (Erin McCarthy).
4. To feather an oar.
5. To feather a propeller.
feather in (one's) cap
An act or deed to one's credit; a distinctive achievement.
feather (one's) nest
To grow wealthy by taking advantage of one's position or by making use of property or funds left in one's trust.
in fine (or good or high)feather
In excellent form, health, or humor.
[Middle English fether, from Old English; see pet- in the Appendix of Indo-European roots.]
feathertop: typical flight feather and a magnified view
bottom: on a Shire horse's leg