hygroscope vs hygrometer

hygroscope and hygrometer both are nouns.

Word	Noun	Adjective	Verb	Adverb
hygroscope	Yes	No	No	No
hygrometer	Yes	No	No	No

As nouns, hygrometer is a hypernym of hygroscope; that is, hygrometer is a word with a broader meaning than hygroscope:

hygroscope: hygrometer that shows variations in the relative humidity of the atmosphere
hygrometer: measuring instrument for measuring the relative humidity of the atmosphere

hygroscope (noun)	hygrometer (noun)
hygrometer that shows variations in the relative humidity of the atmosphere	measuring instrument for measuring the relative humidity of the atmosphere