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]WordNet (r) 3.0 (2006):
hygrodeik n 1: a wet and dry bulb hygrometer