Many words in English have a recognisable internal structure. For example, the word unsuccessful can be broken down into the following three parts:
un + success + ful
The first part, un-, is called the prefix. The second part - success - is a complete word in itself, and is called the base. The last part, -ful, is called the suffix.
Prefixes and suffixes are added to existing words to create new words.
Prefixes are added to the beginning of a word to create a new word. They contribute specific types of meaning. For instance, when we add the prefix pre- to the word 1945, we create a new word pre-1945, meaning before 1945. The following are the main prefixes used in English, together with the kinds of meaning they contribute.