A prefix is a part of a word or a word, within a word. It is put at the start of another word to make a different meaning. It can also mean a number that is put in at the start to show which number something is in a group. It is a type of affix. compound nouns (in other cases also compound adjectives).
The following examples illustrate real prefixes.
Often people want to use a prefix to mean not. There are many prefixes that mean not.
We also learnt the prefixes anti which means against and auto is used to mean self or own
Some examples of these prefixes:
antisocial which means non social
anti glare which means it will prevent sun and light glare on a screen
autograph which means a person's signature
autopilot which means working by itself
Other examples of prefixes:
Scientists and doctors use prefixes in many words.
Sometimes people make up words by adding a prefix. These words are not in a dictionary. But if people use these words enough, sometimes they go into dictionaries. For example, we can make the word unsimple, which splits up into not simple. This is not a word in a dictionary.
Compare to suffix. Suffixes are letters put at the end of a word to change its meaning.
