What is a flibbertigibbet as described in the 1965 musical The Sound of Music?

Shakespeare used the word in King Lear to describe a devil, and Sir Walter Scott used it in Kenilworth to describe a young rascal.

But the meaning Rodgers and Hammerstein intended, a talkative or dizzy person, arose in 1549, in a sermon by Bishop Hugh Latimer for King Edward VI.

Latimer spelled the word flybbertgybe.