"Fahrenheit" is a deprecated form of "Erfahrenheit," which means experience. It is derived from "erfahren," a verb meaning to gain knowledge and the ending "-heit" that is used to turn verbs, adjectives or other nouns into nouns with a similar meaning.
erfahren = to gain knowledge
Erfahrenheit = the state of having gained (a lot of ) knowledge.
Erfahren (verb) and the deprecated "Fahrenheit," themselves are derived from "fahren," which in its original meaning conveyed the idea of travel, and in turn became to mean gaining knowledge of the world. Today "fahren" is almost exclusively used to mean driving.