http://baike.baidu.com/view/67611.htm
From my understanding, single character can be a 'ci yu' or word if it has a its own meaning. So majority of the single characters can be considered as 'ci yu'
1 character is usually known as å—
it is also a è¯�è¯ if it holds its own meaning
2 or more characters combine for a new meaning = è¯� or è¯�è¯
basically, it means "terms", "words".....
nouns are just things, objects, like 人,水,书,飞机,手机,洗衣机,数ç �相机...........
can consist of a few characters.......
è¯�è¯ can also be verbs (动è¯�), adjectives (形容è¯�)........