an affix, e.g. un- in unhappy, placed at the beginning of a word or before a word root: compare infix², suffix¹

a title used before a person's name

to attach (something) as a prefix to a word, etc

to add (something) to the beginning

She prefixed a brief introduction to the article

to add something to the beginning of (something)

He prefixed his speech with a few complimentary remarks