Vocabulary refers to the words we must know to communicate effectively. In general, vocabulary can be described as oral vocabulary (the words we use in speaking or recognize when listening) or reading vocabulary (the words we recognize or use in print).
Vocabulary plays an important part in learning to read. As beginning readers, children use the words they have heard to make sense of the words they see in print. They have a much more difficult time reading words that are not already part of their oral vocabulary.
Vocabulary is also very important to reading comprehension. Readers cannot understand what they are reading without knowing what most of the words mean. As children learn to read more advanced texts, they must learn the meaning of new words that are not part of their oral vocabulary.
Children learn the meanings of most words indirectly, through everyday experiences with oral and written language. They do so by engaging daily in oral language, listening to adults read to them, and reading extensively on their own.
Although a great deal of vocabulary is learned indirectly, some vocabulary should be taught directly. This can be done through specific word instruction (teaching specific words, extended instruction that promotes active engagement with words, and repeated exposure to words in many contexts) and word learning strategies (using dictionaries and other reference aids, using word parts, and using context clues).
Vocabulary instruction should focus on important words (key words to help readers make sense of the text), useful words (words they will encounter often), and difficult words (words with multiple meanings, idiomatic words, etc.).
At least half of the words in the English language are derived from Greek and Latin roots. Knowing these roots helps us to grasp the meaning of words before we look them up in the dictionary. It also helps us to see how words are often arranged in families with similar characteristics.
An affix is a morpheme that is attached to a word stem to form a new word. Affixes may be derivational, like English -ness and pre-, or inflectional, like English plural -s and past tense -ed. They are bound morphemes by definition; prefixes and suffixes may be separable affixes. Affixation is, thus, the linguistic process speakers use to form new words (neologisms) by adding morphemes (affixes) at the beginning (prefixation), the middle (infixation) or the end (suffixation) of words.