an element placed at the beginning of a word to adjust or qualify its meaning (e.g. ex-, non-, re- ) or (in some languages) as an inflection.
a morpheme, not necessarily surviving as a word in itself, from which words have been made by the addition of prefixes or suffixes or by other modification.
a morpheme added at the end of a word to form a derivative (e.g. -ation, -fy, -ing, -itis )