Lexeme

Lexeme is a term in linguistics. They are units of meaning, independent of any inflectional endings, or whether it is one word or several. "Come in" is a lexeme; so is "raining cats and dogs". The largest English dictionaries have about half a million lexemes, though the true figure is likely more.Crystal, David (1995). The Cambridge Encyclopedia of the English Language. Cambridge. p. 119. 

In the English language, run, runs, ran and running are forms of the same lexeme.

A similar concept is the lemma (or citation form). It is the form of a lexeme which is chosen to represent the lexeme, for example, RUN instead of the other forms. Lemmas are used in dictionaries as the headwords. Other forms of a lexeme are usually listed later in the entry. So, all headwords in a dictionary are lexemes.

A lexicon is made of lexemes.

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Category:Language
Category:Linguistics terminology