A term created to fulfill a specific, one-time purpose is known as a nonce word. Even though these are fictitious words, the reader or listener should usually be able to understand the meaning of the nonce word by the way it is formed or through the use of context clues. Most nonce words are only used once, but occasionally, a writer may create one that works its way into common usage. Some of these words even find their way into the dictionary over time.
"Nonce" essentially means "for the one occasion." The word dates back to the Middle Ages, where the phrase "for þe naness" or "for the nonce" came about from misunderstanding the phrase "for þan anes," meaning "for the one." In 1884, the editor of the Oxford English Dictionary, then called the New English Dictionary, created the term "nonce word" to describe any word which was coined for one special, immediate occasion. It is important to note that the term "nonce word" has no relation to the British slang use of "nonce," which refers to a type of sex offender.
Writers frequently create nonce words as a type of placeholder word when looking for a way to express a familiar concept in a new way. Oftentimes, but not always, a writer or speaker creates a nonce word by combining multiple existing words. For example, the term "slithy," coined in Lewis Carroll's Jabberwocky, is a combination of the words "slimy" and "lithe." Other nonce words are formed through the use of onomatopoeia and sound like their intended meaning. "Tattarrattat," coined by James Joyce in Ulysses back in 1922, refers to a knock at the door.
Most nonce words are only used for the single, specific occasion that spawned their creation. Some of these terms do find their way into somewhat common usage, however — especially if the source of their origin is a popular book or movie. For instance, the term "supercalifragilisticexpialidocious" originated from the 1964 musical movie Mary Poppins, but is understood by many even outside the context of the movie as a descriptive term expressing one's enthusiasm for the greatness of a particular subject or event.
On rare occasions, a nonce word may even gain acceptance as an actual word and is eventually included in the dictionary. When this occurs, however, the term does not always mean what it meant during its original coinage. The term "quark," for example, was originally coined in 1939 in James Joyce's Finnegan's Wake. Joyce used the nonce word as a means of describing a certain type of cry. Later, in 1964, the physicist Murray Gell-Mann picked up the term and used it to describe a new type of subatomic particle.