This Discussion is on the definition of word. Many structural grammarian assist the definition, ``minimal free form``. This definition have four problem. First, it is the dependent definition for the inflected languages. Second, the notion of ``free`` is not clear or objective. Third, the ``free form`` often means ``meaningful one``. But there are un-meaningful or rare-meaningful words. Fourth, it is difficult to distinguish empty word-forms from full one in the isolation languages like Chinese. Last two problem is similar in fact. As a word, we have meaningless or semi-meaningless word, which makes a confusion criteria distinguishing word and affix. I suggest the new definition of word that an equivalent basic unit constructing a sentence. A sentence is constructed one subject and one predicate basically. Nouns can be subject. Verb can be predicate. therefore two word group can be recognized as words. If any unit is equivalent with nouns or verbs, the units can be words. The equivalence include the dependent-head relationship. So we can understand the words constructing a sentence are the head of the Phrase or equivalent substitutions. In Korean languages, Chosa, the nominal affix is not word under the this criterion. It have not any substitution word group. It is preferable affix having the ordering of the members. The ordering is big characteristics of affixes. Other dependent unit like dependent nouns or verbs can be words having equivalent substitutions and itself is the head. It can be the just right that a word is a basic unit constructing sentences equivalently.