The Collaborative International Dictionary of English v.0.48:

Fahrenheit \Fah"ren*heit\prop. a. [G.]
   Conforming to the scale used by Gabriel Daniel Fahrenheit in
   the graduation of his thermometer; of or relating to
   Fahrenheit's thermometric scale. Used as an alternative to
   celsius. -- n. The Fahrenheit thermometer or scale.
   [1913 Webster]

   Note: The

   Fahrenheit thermometer is so graduated that the freezing
      point of water is at 32 degrees above the zero of its
      scale, and the boiling point at one atmosphere of pressure
      is 212 degrees. It is commonly used in the United States
      and in England.
      [1913 Webster] faience

WordNet (r) 3.0 (2006):

Fahrenheit thermometer
    n 1: a thermometer calibrated in degrees Fahrenheit