prefix

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To put or attach before or in front of.
2. v. To settle or arrange in advance.
3. v. Grammar To add as a prefix.
4. v. Grammar To add a prefix to.
5. n. Grammar An affix, such as dis- in disbelieve, attached to the front of a word to produce a derivative word or an inflected form.
6. n. A title placed before a person's name.

Century Dictionary and Cyclopedia

1. To fix or put before; place in front; put at the beginning.
2. To fix beforehand; set or appoint in advance; settle beforehand.
3. n. A word or syllable, or a number of syllables, rarely more than two, and usually one (sometimes reduced to a single consonant not forming a syllable), affixed to the beginning of a word, to qualify its meaning or direct, its application: opposed to suffix or postfix, a like addition at the end of a word. A prefix proper is an inseparable element, never used alone, as pre- in prefix, con- in conjure, in- in inactive, un-in unseen, etc.; but prepositions and primitive adverbs used in composition are usually accounted prefixes, as fore- in foresail, down in downfall, in in income, etc. By a looser use such recurring elements as equi-, multi-, iso-, mono-, poly-, etc., in compounds of Latin or Greek origin or formation, are called prefixes, though they are properly independent words in the original language. There is no hard and fast line between a prefix and the initial element of a compound.
4. n. The act of prefixing; prefixion.

Wiktionary

1. n. 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- in conjure.

GNU Webster's 1913

1. v. To put or fix before, or at the beginning of, another thing.
2. v. obsolete To set or appoint beforehand; to settle or establish antecedently.
3. n. That which is prefixed; esp., one or more letters or syllables combined or united with the beginning of a word to modify its signification.

WordNet 3.0

1. v. attach a prefix to
2. n. an affix that is added in front of the word