NOUN (1)

1. a wet and dry bulb hygrometer;

The Collaborative International Dictionary of English v.0.48:

Hygrodeik \Hy"gro*deik\, n. [Gr. ? wet, moist, and ? to show.]
   (Physics)
   A form of hygrometer having wet and dry bulb thermometers,
   with an adjustable index showing directly the percentage of
   moisture in the air, etc.
   [1913 Webster]