gravimeter vs hydrometer

gravimeter and hydrometer both are nouns.

Word	Noun	Adjective	Verb	Adverb
gravimeter	Yes	No	No	No
hydrometer	Yes	No	No	No

As nouns, gravimeter and hydrometer are synonyms defined as:

gravimeter and hydrometer: a measuring instrument for determining the specific gravity of a liquid or solid

gravimeter (noun)	hydrometer (noun)
a measuring instrument for determining the specific gravity of a liquid or solid	a measuring instrument for determining the specific gravity of a liquid or solid
a measuring instrument for measuring variations in the gravitational field of the earth