1) Locomotive part 
A superheater is a device used to convert saturated steam or wet steam into dry steam used in steam engines or in processes, such as steam reforming. There are three types of superheaters namely: radiant, convection, and separately fired. A superheater can vary in size from a few tens of feet to several hundred feet (a few metres to some hundred m...
• (n.) An apparatus for superheating steam.
(from the article `steam engine`) ...the greatest output of work in relation to the heat supplied—is secured by using a low condenser temperature and a high boiler pressure. The steam ...
the part of the boiler where the produced steam is superheated
Su'per·heat`er noun (Steam Engine) An apparatus for superheating steam. 
A device in a steam locomotive that raises the temperature of saturated steam substantially beyond the boiling point of water, increasing power and efficiency.