1. Morpheme —— A morpheme is the smallest meaningful unit of a language. （The smallest functional unit in the composition of words.）
2.Morph—— A morpheme must be realized by discrete units. These actual spoken minimal carriers of meaning are morphs.
3.Monomorphenic words – morphemes are realized by single morphs.
4.Allomorph——Some morphemes are realized by more than one morph according to their position. Such alternative morphs are allomorphemes. E.g. the morpheme of plurality （-s） has a number if allomorphemes in different sound context， e.g. in cats/s/， in bags/z/， in matches/iz/.
5. Free morphemes or Free root —— The morphemes have complete meaning and van be used as free grammatical units in sentences， e.g. cat， walk. They are identical with root words. morphemes which are independent of other morphemes are considered to be free.
6. Bound Morphemes —— The morphemes cannot occur as separate words. They are bound to other morphemes to form words， e.g. recollection （re+collect+ion） collect – free morpheme re-and –ion are bound morphemes. （include bound root and affix） Bound morphemes are found in derived words.
7. Bound root —— A bound root is that part of the word that carries the fundamental meaning just like a free root. Unlike a free root， it is a bound form and has to combine with other morphemes to make words. Take -dict- for example： it conveys the meaning of “say or speak” as a Latin root， but not as a word. With the prefix pre-（=before） we obtain the verb predict meaning “tell beforehand”。 Contradict “ speak against”。 Bound roots are either Latin or Greek.
Although they are limited in number， their productive power is amazing.
8. Affixes —— Affixes are forms that are attached to words or word elements to modify meaning or function. Almost affixes are bound morphemes.
9. Inflectional morphemes or Inflectional affixes —— Affixes attaches to the end of words to indicate grammatical relationships are inflectional， thus known as inflectional morphemes. The number of inflectional affixes is small and stable.
a. There is the regular plural suffix -s（-es） which is added to nouns such as machines， desks.
b. Simple present for the third person singular. –s（-es）
c. The possessive case of nouns. ’s
d. –er and –est to show comparative and superlative degree
e. The past tense marker –ed
f. –ing to form present participles or gerunds.
10. Derivational morphemes or Derivational affixes —— Derivational affixes are affixes added to other morphemes to create new words.
11. Prefixes —— Prefixes are affixes that come before the word， such as， pre+war， sub+sea
12. Suffixes —— suffixes are affixes that come after the word， for instance， blood+y.
13. Root —— A root is the basic form of a word， which cannot be further analyzed without total loss of identity. （What remains of a word after the removal of all affixes.） .e.g. “internationalists” removing inter-， -al-， -ist， -s， leaves the root nation.
14. Stem —— a form to which affixes of any kind can be added. E.g. “internationalists”， nation is a root and a stem as well.
a stem may consist of a single root or two roots and a root plus a affix.
a stem can be a root or a form bigger than a root.