Some words in English are formed using both prefixes and suffixes, for example: "unhelpful". The original word, "help", is called the "base word". Many words will take extra letters both at the beginning and the end to create a new meaning.
Linguistic creativity is responsible for the number of words with prefixes and suffixes. Words can be invented by analogy. If you can "make" or "unmake" a bed, "load" or "unload" a dishwasher, why can't you "befriend" or "unfriend", or "follow" and "unfollow" someone? "Unfriend", in case you hear anyone complaining that it isn't a "real word", was first used in 1659. "Unfollow" hasn't made it into the dictionary, although "unfollowed" has existed as an adjective since 1508, but we immediately understand it because it is created by attaching the un- prefix to the well-known verb, "follow".
Just to make language even more interesting, in English words can be changed in such a way both by adding prefixes to the beginning of a word and suffixes to its ending. Often, as in this quiz, words have both!
Test your knowledge of prefixes and suffixes by playing this quiz.