prefix

Short definition from Wiktionary

Noun

1. 1
   Something placed before another: A morpheme added to the beginning of a word to modify its meaning, for example as, pre- in prefix, con- in conjure, re- in reheat, etc.
2. 2
   Something placed before another: A set of digits placed before a telephone number, to indicate where the number is based, what type of phone number it is (landline, mobile, toll-free, premium rate etc.)
3. 3
   Something placed before another: A title added to a person's name, such as Mr. or Dr.
4. 4
   Something placed before another: An initial segment of a string of characters.

Verb

1. 1
   To determine beforehand; to set in advance.
2. 2
   To put or fix before, or at the beginning of something; to place at the start.