aftershaft

from The Century Dictionary.

• noun In ornithology: A supplementary feather growing out of a feather; the hypoptilum.
• noun The shaft of such a supplementary feather. Also called hyporachis.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) The hypoptilum.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun ornithology An accessory plume arising from the posterior of the contour feathers of many birds.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a supplementary feather (usually small) on the underside of the base of the shaft of some feathers in some birds