Prefix - Wikipedia
https://en.wikipedia.org/wiki/PrefixA prefix is an affix which is placed before the stem of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix un- is added to the word happy, it creates the word unhappy. Particularly in the study of languages, a prefix is also called a preformative, because it alters the form of the words to which it is affixed.