Source : WordNet®

lexeme
     n : a minimal unit (as a word or stem) in the lexicon of a
         language; `go' and `went' and `gone' and `going' are all
         members of the English lexeme `go'

Source : Free On-Line Dictionary of Computing

lexeme
     
         A minimal lexical unit of a language.  {Lexical
        analysis} converts strings in a language into a list of
        lexemes.  For a programming language these word-like pieces
        would include {keywords}, {identifiers}, {literal}s and
        punctutation.  The lexemes are then passed to the {parser} for
        syntactic analysis.
     
        (1996-04-06)