In words from Romanic languages, often it represents reduced forms of Latin ad "to, toward; for" (see ad-), or ab "from, away, off" (see ab-); both of which by about 7c. A prefix is a letter or series of letters attached to the beginning of a word, word base, or suffix to produce a derivative word with a new meaning. 1. not any particular or certain one of a class or group: one at a time; two of a kind; A Miss Johnson called. A third kind of affix is called an infix. Compatible prefixes can work together, as un- and re- in unrefundable. Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020, Collins English Dictionary - Complete & Unabridged 2012 Digital Edition Define prefix: the definition of prefix is an element placed at the beginning of a word to alter or qualify its meaning. First recorded in 1200–50; Middle English; originally preconsonantal phonetic variant of, In both spoken and written English the choice of, Middle English; unstressed preconsonantal variant of, First recorded in 1300–50; Middle English; phonetic variant of, First recorded in 1200–50; Middle English, Middle English, in some words