morpheme

morpheme (morfem): the smallest meaningful linguistic unit. Some words are made up of one morpheme; others of two or more. Morphemes can be lexical (in which case they refer to something), inflectional (in which case they represent grammatical suffixes), or derivational (in which case they represent an affix which changes the meaning and often the word class of the word it is added to). E.g. read (lexical morpheme, stem); reads ('read' + 's' - an inflectional morpheme); unreadable ('un' + 'read' + 'able'; 'un' being a derivational morpheme which creates the opposite meaning of the rest of the word, and 'able' being a derivational morpheme that turns the word into an adjective).