Word (单词)a fundamental unit of speech and a minimum free form; with a unity of sound and meaning (both lexical and grammatical meaning), capable of performing a given function in sentence structures
Morpheme (词素) the smallest meaningful linguistic unit of language, not divisible or analyzable into smaller forms.
allomorphs(词素变体)(s,es)The variant forms of a morpheme as conditioned by position or adjoining sounds
prefix一般改变意思;suffix一般改变词性(ly)
Root (词根)the basic unchangeable part of a word, and it conveys the main lexical meaning of the word.