ther ‧ mom ‧ e ‧ ter /θəˈmɒmətə, θəˈmɒmɪtə $ θərˈmɑːmətər/ BrE AmE noun [countable]
[ Date: 1600-1700 ; Language: French ; Origin: thermomètre , from Greek therme ( ⇨ ↑ therm ) + French -mètre '-meter' ]
a piece of equipment that measures the temperature of the air, of your body etc:
The thermometer registered over 100º C.
a candy/meat thermometer (=used in cooking)