Lexemes are the head-words in a dictionary. 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. "The true figure is undoubtedly a great deal higher".
- Crystal, David 1995. The Cambridge encyclopedia of the English language. Cambridge. p119