We don't have synonyms for reostat yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are rheostat, restat and geostat.
(n) :
Dated form of rheostat. [(electronics, technology) An electrical resistor, with two terminals, whose resistance is continuously variable by moving a knob or slider.]
(n) :
Dated form of rheostat. [(electronics, technology) An electrical resistor, with two terminals, whose resistance is continuously variable by moving a knob or slider.]