ther ‧ mo ‧ stat /ˈθɜːməstæt $ ˈθɜːr-/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Origin: thermo- + -stat 'instrument for keeping something steady' (from Greek -states , from histanei 'to cause to stand' ) ]
an instrument used for keeping a room or a machine at a particular temperature