In linguistics, a nonce word—also called an occasionalism—is any word (lexeme), or any sequence of sounds or letters (phonemes or graphemes), created for a single occasion or utterance but not otherwise understood or recognized as a word within a given language. Nonce words have a variety of functions and are most commonly used for humor, poetry, children's literature, linguistic experiments, psychological studies, and medical diagnoses, or they arise by accident.
Some nonce words have a meaning at their inception or gradually acquire a fixed meaning inferred from context and use, but if they eventually become an established part of the language (neologisms), they stop being nonce words. Other nonce words may be essentially meaningless and disposable (nonsense words), but they are useful for exactly that reason—the words wug and blicket for instance were invented by researchers to be used in child language testing. Nonsense words often share orthographic and phonetic similarity with (meaningful) words, as is the case with pseudowords, which make no sense but can still be pronounced in accordance with a language's phonotactic rules. Such invented words are used by psychological and linguistic researchers and educators as a tool to assess a learner's phonetic decoding ability, and the ability to infer the (hypothetical) meaning of a nonsense word from context is used to test for brain damage. Proper names of real or fictional entities sometimes originate as nonce words.
The term is used because such a word is created "for the nonce" (i.e., for the time being, or this once), coming from James Murray, the first editor of the Oxford English Dictionary.:25 Some analyses consider nonce words to broadly fall under neologisms, which are usually defined as words relatively recently accepted into a language's vocabulary; other analyses do not.