Word can be defined as a meaningful group of letters printed or written horizontally across a piece of paper. As defined in terms of spoken language,a word is viewed as a sound or combination of sounds,which are made voluntarily with human vocal equipment. According to semanticists,a word is a unit of meaning. According to grammarians,a word is a free form that can function in a sentence. To sum up,the definition of a word will cover the following points:
(a)a minimal free form of a language
(b)a sound unity
(c)a unit of meaning
(d)a form that can function alone in a sentence
Map and money are simple words while revolution and blackmail are complicated words. No matter what words are,all must comply with these criteria above(张维友,2004:2).