-stat

The terminal element in certain names of scientific instruments, employed on the analogy of early coinages from other languages, namely heliostat (from the New Latin hēliostata, itself apparently representing an assumed Ancient Greek etymon of the form *ἡλιοστάτης (hēliostátēs), from ἥλιος (hḗlios, “sun”) + -στατης (-statēs), the latter an agent-nominal suffix from the aorist active participial stem (the στα- (sta-) root) of ἵστημι (hístēmi, “to cause to stand”, “to set”)), siderostat (from the Latin sīdus, star + the Ancient Greek -στατης (-statēs)), and aerostat (from the French aérostat, itself a back-formation from aérostatique (formed after hydrostatique), formed on the analogy of héliostat); later coinages have been formed on the analogy of heliostat, apparently with some reference to the Ancient Greek στατός (statós, “standing”, “stationary”). See also clinostat, hydrostat, and thermostat.

来源：wiktionary