Definition of prefix:
that which is prefixed; especially one or more letters or syllables added to the beginning of a word to modify its meaning; as, pre-
in prefix, con-
put or fix before, or at the beginning of, another thing; as, to prefix a syllable to a word, or a condition to an agreement; set or appoint beforehand; settle or establish antecedently. [Obs.]
"prefixed bounds. --Locke."