How do you spell Plumule

Available Definitions:
1)  n. - The first bud, or gemmule, of a young plant; the bud, or growing point, of the embryo, above the cotyledons. See Illust . of Radicle.
2)  n. - A down feather.
3)  n. - The aftershaft of a feather. See Illust . under Feather.
4)  n. - One of the featherlike scales of certain male butterflies.