A thermometer measures a person/s body temperature. This might be under the tongue or under the arm in the armpit/ Don't get thermometer mixed up with a tempometer. Best write it as tempo meter, two words, and in fact this is correct. A tempo meter checks the speed, or tempo, of a piece of music. Tempo just means time.
Hydrometers measure the relative density of liquids - something much more advanced in your study of science. A gyrometer indicates continuously the number of revolutions of a rotating axis. Advanced, yes, but a gyroscope is great fun to play with and fascinating to watch. it will help you understand this aspect of physics.