prefix

noun
  1. A prefix is a group of letters added to the beginning of a word to change its meaning or form a new word. noun
    The prefix 'un-' in 'unhappy' changes the meaning of the word to its opposite.
    Adding the prefix 'pre-' to 'view' forms the word 'preview'.
  2. To add a prefix to a word, thereby altering its meaning or creating a new word. verb
    In English, you can prefix 're-' to 'write' to form 'rewrite'.
    Teachers often instruct students on how to prefix words correctly to expand their vocabulary.