flibbertigibbet \FLIB-ur-tee-jib-it\ (noun) - A silly, flighty, or scatterbrained person, especially a pert young woman with such qualities.
"I'll bat my eyelashes and pretend to be a flibbertigibbet wandering the house in search of the retiring room." -- Sabrina Jeffries, 'Never Seduce a Scoundrel'
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Flibbertigibbet is from Middle English flipergebet, which is probably an imitation of the sound of meaningless chatter.