The Collaborative International Dictionary of English v.0.48:

Superheat \Su`per*heat"\, v. t. [imp. & p. p. Superheated; p.
   pr. & vb. n. Superheating.]
   1. To heat too much, to overheat; as, to superheat an oven.
      [1913 Webster]

   2. (Steam Engine) To heat, as steam, apart from contact with
      water, until it resembles a perfect gas.
      [1913 Webster]

   3. To heat (a liquid) above its boiling point without
      converting it into vapor.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Superheated \Su"per*heat`ed\
   heated to a temperature above the boiling point at the
   ambient pressure; -- said of liquids. In such an unstable
   condition, a small disturbance of the liquid can cause a
   rapid and sometimes violent ebullition of vapor.
   [PJC]