Source : Webster's Revised Unabridged Dictionary (1913)

Rheostat \Rhe"o*stat\, n. [Gr. "rei^n + stato`s standing still.]
   (Elec.)
   A contrivance for adjusting or regulating the strength of
   electrical currents, operating usually by the intercalation
   of resistance which can be varied at will. --Wheatstone.
   --{Rhe`o*stat"ic}, a.

Source : WordNet®

rheostat
     n : resistor for regulating current [syn: {variable resistor}]