A lexeme represents the most basic building block of a language. If you open a typical dictionary, the entries there are lexemes. Most lexemes have variations which build upon its most basic form. Thus, the lexeme walk could vary in form, such as in walks, walked, and walking. The lexeme slow also varies in form: slower, slowest, slowly.
A lexeme can thus be broken down into two large categories: invariable lexemes and variable lexemes. An invariable lexeme means that there is only one form of the word; it isn't altered in any way for meaning. The and a are examples of invariable lexemes. Variable lexemes, then, do exist in numerous forms. The word pretty is variable, as it also takes the forms of prettier and prettiest. The word be also takes the forms am, is, are, was, were, being, and been.
Sometimes a lexeme consists of more than one word because the meaning relies on a combination of words. Fire station is one example of a multiword lexeme. Phrasal verbs also represent this combination of words as one lexeme: pick up, put away, pass out, and look out.
A language's idioms are anther example of its lexemes. The meaning of this lexeme depends on an understanding of those words based in usage that does not break down into a literal translation. In English, some of those lexemes include the following:
- think outside the box
- change of heart
- piece of cake
- cutting corners
- the last straw