noun

• (linguistic morphology) A bound morpheme added to a word’s stem, such as a prefix or suffix.
  "A prefix is an affix that joins to the beginning of another word. Depending on the prefix, it can slightly or significantly alter the meaning of a word. For example, the English prefix “un-” changes a word into its opposite, as from “do” to “undo,” altering its meaning entirely."
• (now uncommon) That which is affixed; an appendage.
• (mathematics) The complex number a+bi associated with the point in the Gauss plane with coordinates (a,b).
• (decorative art) Any small feature, as a figure, a flower, or the like, added for ornament to a vessel or other utensil, to an architectural feature.

verb

• (transitive) To attach.
  "to affix a stigma to a person"
• (transitive) To subjoin, annex, or add at the close or end; to append to.
  "to affix a syllable to a word"
• (transitive) To fix or fasten figuratively; with on or upon.
  "eyes affixed upon the ground"