n. In ornithology, a down-feather; a feather of plumulaceous structure throughout.n. In entomology: A little plume-like organ or ornament.n. One of the peculiar obcordate scales found on the wings of certain lepidopterous insects, as Pieridæ.n. The bud of the ascending axis of a plant while still in the embryo, situated at the apex of the caulicle (or radicle), above the base of the cotyledon or cotyledons, and inclosed by them when there are two or more.