This is the chronicle of how I started out researching the word "flibbertigibbet" and ended up finding a selcouth pun of Shakespeare's from King Lear that's lain undiscovered by all but one or two people since 1603, amongst other things.
The Castle of Perseverance, a medieval morality play written around 1425, is notable for having the first recorded instances of the words flepergebet, flypyrgebet, and flepyrgebet, which were to crystalise later as flibbertigibbet. The OED records this origin as being "apparently an onomatopœic representation of unmeaning chatter" and gives its foremost meaning as a chattering or gossiping person. But in 1603, Samuel Harsnett, the forty-two year old then Vicar of Chigwell, used Fliberdigibbet (with a "d") in his hilarious polemic A Declaration of Egregious Popish Impostures to denote not a gossiping fishwife, but a demon.
Entered in the Stationers' Register on the 16th of March, the Declaration is a retort at the actions of Catholics at the time who were using possession by demons and subsequent exorcisms as methods to frighten the public into Catholicism. Chapter Ten is a deposition of "the ſtrange names of their deuils", and contitutes an extraordinary nomenclature bazaar: Maho, Modu, Pippin, Philpot, Hilco, Smolkin, Hillio, Hiaclito, Lustie huffe-cap, Soforce, Cliton, Bernon, Hilo, Motubizanto, Killico, Hob, Portirichio, Frateretto, Fliberdigibbet, Hoberdidance, Tocobatto, Lustie Jollie Jenkin, Delicat, Puffe, Purre, Lustie Dickie, Cornerd-cappe, Nurre, Molkin, Wilkin, Helcmodion, and Kellicocam.
Note that not only Fliberdigibbet is lifted from comic colloquial words of the time, but Hoberdidance too. Michael Quinion, in his treatment of the word hobbledehoy suggests that "it may well be related to Hoberdidance or Hobbididance, which was the name of a malevolent sprite associated with the Morris dance (and whose name is from Hob, an old name for the Devil; nothing to do with hobbits)." In fact, Tolkien subconsciously took the word hobbit from a list of untoward creatures even more staggering than Harsnett's in a piece in The Denham Tracts by Michael Aislabie Denham, so "hobbit" and "Hob" are indeed related. Denham himself called his staggering piece "Ghosts Never Appear on Christmas Eve!", which is a reference, of course, to Hamlet.
Shakespeare evidentally took to Harsnett's list of demons as he used several of them in King Lear, in Act III Scenes iv and vi. Specifically, Edgar, feigning the madness of a Tom O'Bedlam, mentions Smulkin (Smolkin), Obidicut (Haberdicut), Hobbididence (Hoberdidance), Mahu (Maho), Modo (Modu), Flibbertigibbet (Fliberdigibbet), Frateretto, and Hoppedance (Hoberdidance). In trying to find out more about this list, I came across an apparently unheeded observation by Thomas Alfred Spalding in his 1880 work Elizabethan Demonology that deserved further investigation:
In addition to these, Killico has probably been corrupted into Pillicock—a much more probable explanation of the word than either of those suggested by Dyce in his glossary; and I have little doubt that the ordinary reading of the line, "Pur! the cat is gray!" in Act III. vi. 47, is incorrect; that Pur is not an interjection, but the repetition of the name of another devil, Purre, who is mentioned by Harsnet. The passage in question occurs only in the quartos, and therefore the fact that there is no stop at all after the word "Pur" cannot be relied upon as helping to prove the correctness of this supposition. On the other hand, there is nothing in the texts to justify the insertion of the note of exclamation.
It is also on Spalding's word alone that I take Obidicut to be a derivation of Harsnett's "Haberdicut", since I was unable to find Haberdicut in the Declaration myself. But as to the observations of Spalding quoted above, I note firstly that in place of his suggestion that Pillicock is a corruption of Killico, the more likely source is either Kellicocam or a portmanteau of Killico and Kellicocam. In the quartos, Edgar is recorded to say "Pilicock ſate on pelicocks hill", even though the First Folio normalises this—or perhaps records this more accurately—as "Pillicock sat on Pillicock hill". Killico may have the vowels of the First Folio, but only Kellicocam has the "cock" sound. It is most likely too, of course, that the former is an abbreviation of the latter.
But the Pur claim is much more fascinating, and I wanted to corroborate Spalding's claim. On a close examination of Harsnett's work, page 50, it seemed to me that the word used couldn't possibly be Purre since the context of its use was "Puffe, and ?urre" where the ? denotes an italicised capital letter that's different from the clear P of Puffe, but that is somewhat difficult to make out. If it turned out to be an F, it might have made sense for Pur to be a pun on Puffe and Furre, but in comparing it to both other instances of F and T, it didn't fit. Then it dawned on me that initial capital letters used a different, more lavish, glyph and that for some reason the typographer had used an initial italic P here even though it wasn't initial. This was affirmed by the use of the same glyph earlier on in the work, on page 21, in the name of "Sir George Peckham". It's used inconsistently there too.
I then went to the trouble of examining each of the five quartos of King Lear that the British Library has published online. In each one the phrase is exactly the same, as it occurs in the last line of the following:
Ed. Let vs deale iuſtly, ſleepeſt or wakeſt thou iolly ſhepheard,
Thy ſheepe bee in the corne, and for one blaſt of thy minikin
mouth, thy ſheepe ſhall take no harme, Pur the cat is gray.
The capitalisation after a comma reinforces Spalding's conjecture to a point where I think the modern interpretation, which every version that I can find uses, of "Pur! the cat is gray" on a new line is entirely erroneous; Pur is the name of the demon, and hence a pun on the sound of the cat-like shape that it's assumed. There's such a long chain of bad editorialisations of Shakespeare from before Warburton and onwards that it's important to remember that we're just at the latest stage of understanding, and not the goal.
Incidentally, in the Halliwell-Phillipps (C.34.k.17) quarto of 1608, an annotator has gone through amending some of the errors in the text, and has occasionally underlined a passage. "Pur the cat is gray" is one of those passages which has been underlined, though for what reason it's difficult to tell.
It occurred to me that the list of names in the Declaration may also help to clear up the strange word of Edgar's which is given first (III.iv) as "Seſey" in the First Folio and in quartos one, two, and three as "caese", "cease", and "ceas"; and second (III.vi) as "seſe" in the First Folio only. It's amended by contemporary editors as "Sessa!", which is an interjection that some take as meaning "be off with you!", and which has its canonical spelling taken from the only other possible use, in I.i of The Taming of the Shrew. On this mysterious word, the OED reports:
[perh. var. of SA, SA, or possibly a. F. cessez 'cease!' It is not certain that modern editors are right in inserting the form sessa in all the passages; the word may not be the same in the three places.]
1. An exclamation of uncertain meaning.
The cessez idea is from Dr. Johnson in his notes on King Lear. On "Dolphin my Boy, Boy Sesey" specifically, Dr. Johnson insightfully comments that "of this passage I can make nothing. I believe it corrupt: for wildness, not nonsense, is the effect of a disordered imagination." The closest match in Harsnett for Sesey is Soforce, and for Dolphin Delicat, but I believe both too far removed to merit too serious a consideration. At best, it is possible that Shakespeare had invented another name as far removed as Obidicut is from Haberdicut, but that it's now lost to us due to the transcription errors for which the scriveners of the time were well known. Compare, for example, how in one of the first quartos (C.34.k.17) Flibbertigibbet is Sriberdegibet (or Sriberdegibit), in another it's Sirberdegibit, and in both Smulkin is the rather wonderful "snulbug".
Snulbug could even be a word from Shakespeare own pen, later changed to accord more closely to Harsnett's original. Even though for centuries we have tried, in the words of H.H. Furness, to "comprehend each syllable that is uttered, or strain our ears to catch every measure of the heavenly harmony, or trace the subtle workings of consummate art" from Shakespeare, it's a shame and a relief that we'll always have a long way to go.