Neologisms can be divided in three categories/phases:
- Unstables: Those that belong to this category are the newest ones, as in being just introduced, or that are used by few.
- Spread: As the name says, they are spread enough, so they are used by a wide number of people, but are not accepted as "normal" words yet.
- Stables: Those who get accepted by the public audience and start to be used like other words become stable.
Anyway, although we can say that when a word goes inside the Dictionaries, it is not a neologism anymore, if it's being used so commonly and widely, it will be considered a normal word like others, and this is what counts.
Sometimes, even when experts or linguists don't agree on some neologism, for various reasons, what really matters is the common usage and the acceptance by the public audience, as you could also see from the three categories/phases I wrote above.
If the event/situation the neologism describes cease to exist, the word will stop being used and therefore disappear. This is to answer to your second question.
More than what was asked, but below is a near-copy of an etymological answer I left on math.SE a while ago, on the etymological origin of the words "zero", "cipher", and "nought". (Sources: Online Etymology Dictionary and Oxford English Dictionary.)
zero: circa 1600, (either from Middle Latin zephirum, or French zéro or its source Italian zero, for *zefiro) in any case from Arabic sifr "cipher", itself a translation of Sanskrit śūnya "empty place, desert, naught".
cipher: late 14th century, from Arabic sifr, "zero", literally "empty, nothing", from safara "to be empty", loan-translation of Sanskrit śūnya "empty". The word "cipher" came to Europe with Arabic numerals. Originally meant "zero", then "any numeral", then (c. 1520s) "coded message". OED: "The Arabic was simply a translation of the Sanskrit name śūnya, literally ‘empty’."
nought: variant of naught which means "nothing". The meaning of "zero, cipher" is only from the early 15th century. (?c1425 Crafte Nombrynge in R. Steele The Earliest Arithmetics in English. (1922) 20: "A 0 is noȝt, And twyes noȝt is but noȝt.")
So these sources seem to agree that:
- In Sanskrit, the word for "empty" (śūnya) was used for zero.
- Correspondingly when translating into Arabic, the word sifr based on the word safara, meaning "to be empty", was used for zero.
- For the number in English, cipher and zero were imported from Arabic, but also, similar to the passing from Sanskrit to Arabic, the existing word for "nothing" (nought) was used.
Best Answer
Interestingly, the word already existed as far back as 1681, and originally meant:
So it was basically an alternative form to "idiosyncrasy" and was just re-appropriated for its other meaning.
However, even more interestingly, I see a reference from the OED to the use of this word with the current interpretation of "idiot form of government" (made by an author named Thomas Sinclair) from all the way back in 1878 (and my sincere apology for the unfortunate fact that the cited quotation is antisemitic):
Great question; I was surprised by what I discovered.