What is that which is prefixed; esp., one or more letters or syllables combined or united with the beginning of a word to modify its signification; as, pre- in prefix, con- in conjure called?

prefix — That which is prefixed; esp., one or more letters or syllables combined or united with the beginning of a word to modify its signification; as, pre- in prefix, con- in conjure. (Webster's 1913.)