psychrometer

/saɪˈkrɑmɪtər/
noun
  1. An instrument that measures the amount of water vapor in the air, usually by comparing the temperatures of a wet bulb and a dry bulb thermometer.
    • In science class, we built a simple psychrometer to measure the moisture in the classroom air.
    • Farmers often rely on a psychrometer to decide the best time for irrigating their crops.
    • The meteorologist used a psychrometer to check the humidity before the storm.