nonword

Nonword is a term used in linguistics and cognitive science to refer to a sequence of letters or sounds that does not correspond to a word in a language’s lexicon. Nonwords may be pronounceable or illegible, and they often resemble real words in structure, following the language’s phonotactic rules.

Related terms include pseudoword (or nonce word) for a pronounceable nonlexical item, and nonce word for a word coined for a single occasion. A nonword may be legally pronounceable yet carry no established meaning in the language.

In psycholinguistics, nonwords are used to study how readers and speakers process phonology, orthography, and lexical access. Tasks such as reading aloud, spelling, or lexical decision use real words alongside nonwords to gauge response times and accuracy. Nonwords that conform to the language’s phonotactics (pseudowords) are particularly informative about decoding.

In computational linguistics and natural language processing, nonwords can refer to out-of-vocabulary items—strings not found in a system’s lexicon. They reveal weaknesses in language models, help test spellcheckers, or serve as controlled inputs in evaluation benchmarks.

Because what counts as a nonword depends on the language’s orthography and phonology, cross-language comparisons require careful definition. Examples in English include "blick" or "ploff"; unpronounceable strings like "xqz" also count as nonwords.