A text: Persons who are pluming themselves on having detected a vulgar error that they can amend are not likely to admit that it is a mare's nest on the unreasoned ipse dixit of an eighteenth century rhetorician, or even of a twentieth century OED.
I've consulted several dictionaries, and they all do not have a verb like PLUME; could you tell me what the red words mean?
verb (used with object)
11. to furnish, cover, or adorn with plumes or feathers.
12. (of a bird) to preen (itself or its feathers).
13. to feel complacent satisfaction with (oneself); pride (oneself) (often followed by on or upon ): She sat before the mirror, pluming herself upon her beauty.