In psychiatry, the term, neologism, is used to describe the use of words that only have meaning to the person who uses them, independent of their common meaning. This is considered normal in children, but a symptom of thought disorder (indicative of a psychotic mental illness, such as schizophrenia) in adults.
People with autism also may create neologisms.
In theology, a neologism is a relatively new doctrine (for example, rationalism). In this sense, a neologist is an innovator in the area of a doctrine or belief system, and is often considered heretical or subversive by the mainstream clergy or religious institution(s).
Neologisms tend to occur more often in cultures that are changing rapidly and also in situations where there is easy and fast propagation of information. The new terms are often created by combining existing words (see compound noun and adjective) or by giving words new and unique suffixes or prefixes. Portmanteaux are combined words that begin to be used commonly. Neologisms also can be created through abbreviation or acronym, by intentionally rhyming with existing words or simply through playing with sounds.
Neologisms often become popular through memetics–by way of mass media, the Internet, and word of mouth (including academic discourse in many fields, renowned for the use of distincitve jargon, with recent coinages such as Fordism, Taylorism, Disneyfication and McDonaldization–now in everyday use). (See also Wiktionary's Neologisms:unstable or Protologism pages for a wiki venue of popularizing newly coined words). Every word in a language was, at some time, a neologism, ceasing to be such through time and acceptance.
Neologisms often become accepted parts of the language. Other times, however, they disappear from common use just as readily as they appear. Whether a neologism continues as part of the language depends on many factors, probably the most important of which is acceptance by the public. Acceptance by linguistic experts and incorporation into dictionaries also plays a part, as does whether the phenomenon described by a neologism remains current, thus continuing to need a descriptor. It is unusual, however, for a word to enter common use if it does not resemble another word or words in an identifiable way. (In some cases, however, strange new words succeed because the idea behind them is especially memorable or exciting.)
When a word or phrase is no longer "new", it is no longer a neologism. Neologisms may take decades to become "old", however. Opinions differ on exactly how old a word must be, to cease being considered a neologism; cultural acceptance probably plays a more important role than time in this regard.
Newly-created words entering a language tend to pass through stages that may be described as,
For a list of topically arranged protologisms (very-recently-coined terms), see Wiktionary:List of protologisms by topic.
See also Political neologisms
Words or phrases created to make some kind of political or rhetorical point, sometimes perhaps with an eye to the Sapir-Whorf hypothesis include,
Sometimes the title of a book will become the neologism, for instance, Catch-22 (from the title of Joseph Heller's novel). Also worthy of note is the case in which the author's name becomes the neologism, although the term is sometimes based on only one work of that author. This includes such words as "Orwellian" (from George Orwell, referring to his novel Nineteen Eighty-Four) and "Ballardesque" or "Ballardian" (from J.G. Ballard, author of Crash). Kurt Vonnegut's Cat's Cradle was the container of the Bokononism family of nonce words.
Another category is words derived from famous characters in literature, such as "quixotic" (referring to the titular character in Don Quixote de la Mancha by Cervantes), a "scrooge" (from the main character in Dickens's A Christmas Carol), or a "pollyanna" (from Eleanor H. Porter's book of the same name). James Joyce's Finnegans Wake, composed in a uniquely complex linguistic style, coined the words monomyth and quark.
Lewis Carroll's poem "Jabberwocky" has been called "the king of neologistic poems" because it incorporated dozens of invented words. The early modern English prose writings of Sir Thomas Browne are the source of many neologisms as recorded by the OED.