PREFIX
1. A term in WORD-FORMATION for an AFFIX added at the beginning of a word or base to form a new word: re- added to write to form re-write/rewrite.

2. A general term for a word, letter, number, or other item placed before something else: the letter A in the sequence A133; the COMBINING FORM auto- prefixed to biography to form autobiography.

Productivity

A prefix is productive when it contributes to the meaning of a word (the un- in unhappy having the meaning ‘not’) and can be added freely to other, comparable words (unable, unkind). It is non-productive when it occurs in a word but does not contribute to its meaning: con- in condition. The meaning of the word condition is unrelated to the union of con- and -dition and there is no independent base word *dition. A prefix is vestigial when only a trace of it can be detected by scholars: the s of spend, which was once expend. The same prefix may be productive in some words (dis- in disconnect, dislocate), non-productive in others (dis- in disaster, distribute), and vestigial in others still (sport, once disport). There are ‘twilight’ states: re-when productive means ‘again’ (redo, reconnect) and when non-productive (as in remiss) has no meaning, but in *rejuvenate, *repair the meaning ‘again’ is present even though the bases to which re- attaches (juvenate, pair) are not independent words.

Provenance

The prefixes of English derive from: (1) OLD ENGLISH: a- in asleep, be- in bespatter, un- in unready. (2) FRENCH: dis- in disappear, mis- in misgovern. (3) LATIN: ante- in anteroom, in- in inactive, pre- in preconceive. (4) GREEK: a- in amoral, anti- in anti-war, meta- in metaphysical. Prefixes with different backgrounds can, however, fall into relational sets: vernacular over-, as in over-sensitive more sensitive than necessary or desirable; Latin super-, as in supersensitive very sensitive (especially of instruments, film, etc.); Greek hyper-, as in hypersensitive excessively sensitive (especially to allergens). The negative prefixes of English form a range of usages that are sometimes irregularly paired (ungrateful/ingratitude, unlikeable/dislike, unstable/instability), are sometimes a source of confusion (disinterested/uninterested), and are sometimes delicately contrastive (unmoral, immoral, amoral, non-moral).

Pairing

In English, SUFFIXES often occur in chains (such as the -istically in characteristically), but prefixes do not. They usually occur singly (un- in unhappy, re- in re-write), but sometimes occur in pairs: un-, re-, in unremarried not married again; anti-, dis-, in antidisestablishment. In these examples, both prefixes are productive (that is, married and establishment are independent base words), but pairing is commonly the addition of a productive to a non-productive prefix: productive in- to non-productive re- in irredeemable (no *deemable); in- added to con- in inconclusive (no *clusive). Sometimes, the same prefix may be added twice, usually with a hyphen: meta-metalanguage, re-reconstructed, co-conspirator (the productive co-beside the non-productive con-). Very occasionally, a three-prefix chain occurs: non-reproductive, in which non- is fully productive, re- is partly productive (reproduction being more than an extension of production), and pro- is non-productive (no *ductive).

pre·fix / ˈprēˌfiks/ • n. a word, letter, or number placed before another: add the prefix 83 to the extension number. ∎  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 title placed before a name, e.g., Mr.• v. [tr.] add (something) at the beginning as a prefix or introduction: a preface is prefixed to the book. ∎  add a prefix or introduction to (something): all three-digit numbers will now be prefixed by 580.DERIVATIVES: pre·fix·a·tion / ˌprēfikˈsāshən/ n.

prefix verbal element placed before and in combination with another XVII; title prefixed XIX. — modL. præfixum, sb. use of n. of præfīxus, pp. of L. præfīgere fix in front; see PRE-, FIX.
So vb. XV. — (O)F. préfixer.

prefix of a string α. Any string β where α is the concatenation βγ for some string γ. Thus in coding theory, a word is said to be a prefix of another word if the former word matches the first symbols of the latter. See also prefix codes.