What is the X in X-mas?
late 14c., "a feather" (especially a large and conspicuous one), from Old French plume "soft feather, down; feather bed," and directly from Latin pluma "a feather, down; the first beard," from PIE root *pleus- "to pluck; a feather, fleece" (cf. Old English fleos "fleece"). Meaning "a long streamer of smoke, etc." is first attested 1878.
late 14c., "to pluck, strip," from plume (n.). From mid-15c. as "to adorn with plumes." Meaning "to dress the feathers" is from 1702. Related: Plumed; pluming.