A prefix is a letter or set of letters that compose a linguistic unit called affix and that is added before a word to create a new word. Prefixes differ from suffixes because they are always placed before and not after a word, but similar to suffixes prefixes change the meaning of words and most of them are derived from other languages including Greek and Latin. In the case of the prefix, "ex-" this prefix derives from Latin and means "out of" and "from", but can also mean "not" or "without". For example, in the word "exhale" means to breath out or the word "ex-soldier" means from the soldiers but also indicates a previous stated. Considering this, the best definition for the prefix "ex-" is "out or from".
