hypoptilum

Century Dictionary and Cyclopedia

1. n. In ornithology, the aftershaft or hyporachis of a feather; the whole of the supplementary plume which springs from the stem of the main feather at the junction of calamus and rachis. Hypoptila are usually present in the general plumage of birds, but are wanting in some families, as owls, and are never developed on the remiges or rectrices. They are usually much smaller than the main feather, but in some cases are about as large, when the feather appears to be double, but with a single barrel. See hyporachis and aftershaft, both of which are more frequently used than hypoptilum.

Wiktionary

1. n. ornithology An aftershaft.

GNU Webster's 1913

1. n. (Zoöl.) An accessory plume arising from the posterior side of the stem of the contour feathers of many birds; -- called also aftershaft. See Illust. of feather.