Lexemes

A lexeme is the abstract unit of a language’s lexicon that encompasses all the inflected forms sharing a single meaning and syntactic category. The set of forms associated with a lexeme constitutes its paradigm. For example, the English verb run has the forms run, runs, ran, running, which are different surface realizations of the same lexeme. The form running is not a separate lexeme; it is a realization of the run lexeme.

In dictionaries, the canonical form used to represent a lexeme is the lemma; for the verb run, the lemma is run. The lexeme thus corresponds to the underlying meaning and grammatical category, while actual words in sentences are word forms or inflected realizations of that lexeme.

The concept helps distinguish meaning from morphophonology: many languages group together all inflected variants under a single lexeme, even though those variants may display different morphosyntactic properties. Different senses or related words may be treated as separate lexemes when they deserve distinct entries in the lexicon.

In linguistic research and natural language processing, lemmatization maps each word form to its lexeme, aiding tasks such as indexing, concordancing, and parsing. The term is used across languages, though the precise boundaries between a lexeme and its forms can vary with morphology, derivation, and compounding.